@Other Aaron Now we're cooking with gas.
So first, top layering should generally work out: baselayer, insulating layer, shell layer. In winter, a lot of people split into their "rest/emergency" insulation so it can be down, packable, and make moisture less of an issue. Then they've got their "active" layer that they're physically moving uphill in, maybe layering under their shell for the ski down. Likewise, I generally recommend different "active" insulation for inbounds and out since you're wearing a shell the full time for the former and generally not until the descent for the latter. On bottom, generally a baselayer and then choice of softshell vs hardshell (unless someone has an overpant)
Your kit is missing a lot of the important building blocks and instead there's a lot of hybrid gear, which often struggles to adequately check a box across those specific layering needs. I can see why you've got comments of being both sweaty and cold over the course of a tour, and why you've got 4 jackets in the pack. I'm going to try not to turn this into a novel, but I'm gonna walk through my & my partner's typical layering and the strategy that went into it, then answer some of your questions and poke at a few things in your jacket quiver. Anytime I'm mentioning weight, I'm finding the men's equivalent to my pieces.
Resort (her): merino base layer (insulates when wet, so does a great job with start/stop activities). Polar fleece that is insanely poor quality and thin from Kari Traa. Like could've gotten something better from Walmart or Amazon Essentials. Polar fleece is extremely air & vapor permeable. It's a knit (think open loops like a t-shirt) instead of a woven (criss-crossed fabric in a loom like a dress shirt or jeans or a hardshell). Knits use a lot less thread per surface area and those loops let air and vapors through easily. Most midlayers are wovens or even have a wind-resistant treatment on it, which seals all that vapor in like a plastic bag (as if hardshells aren't giving enough plastic bag effect on their own). Armada Resolution hardshell - almost matches the Mission specs to a T. 3L Gore, pit zips, freeride fit. Pants are a 3L Gore with good venting.
Resort (him): Merino 150 Smartwool long sleeve top, Flylow 3L shell, most similar to the Malone. Bibs are Flylow Bakers.
Winter touring (her): Dakine Callahan Fleece base layer. Generally, you want your base layer to be super thin since thinner dries faster. But Libolon pulled some serious wizardry as the fabric supplier and it keeps me from futzing around with a midlayer as much. But I tend to carry a Marmot Ether DriClime jacket (8.5g for the old hoodless version) since it takes up less room than a fossilized Clif bar at the bottom of my pack. It's essentially a Houdini jacket (thin nylon woven) with the thinnest little fleece backer. Underarms swap nylon for a mesh. Blocks just enough wind and adds the tiniest bit of heat. Saw it also highly recommended on a few Rainier summit blogs as a great active layer for the first ~3k out from Muir in the morning. Belay jacket (Rab Infinity Endurance, 20 oz) for a rest/emergency layer. 850 fill, super compressible. Hydrophobic down & good moisture resistance inside and out. Pertex Quantum endurance face keeps oils out, moisture out, protects from tears & abrasion, and also blocks the wind - un-treated face fabrics don't trap warm air as well when it's blustery. Shell's the same 3L gore pieces from the resort.
Winter touring (him): Smartwool 150 t-shirt under a Columbia tech flannel. The t-shirt wicks from all the sweaty spots, but the tech flannel's woven and blocks a little more wind than a LS base layer woul. It's really rare I see him put on anything else for the uphill. If I do, it's an OR Ascendant (11 oz), which is super similar to my Marmot, but the fleece backer has a little more loft. Rest / emergency insulation is either the same Rab Infinity Endurance or a mid-weight 800 fill Marmot puffy that's ~15 years old and very behind from a textile innovation standpoint, but also not dead yet. Same shell as the resort. Swaps the Baker bibs that are generously cut and a thick polyester face for the OR Hemispheres since they're a lot lighter and have stretch.
Spring Ski Mountaineering (her): Sun hoody, Marmot Ether Driclime active insulation layer. Either the Rab belay puff or the Cerium LT (which sadly does not have wind resistance) for a summit & snack layer. Swap my resort shell for an all-around alpine shell (old Beta LT with Gore Pro membrane) and my hardshell pant for a super breezy softshell (Procline FL).
Spring Ski Mountaineering (him): Sun hoody, OR Ascendant, same 2 puffy options from winter, swaps the resort shell for an old version of the Marmot Alpinist (gore pro). Usually stays in the Hemispheres until true summer where he'll swap to a softshell.
We mainly swap out base layers & shells depending on how warm it is and how much packability we need with crampons or glacier gear. Both types of insulation layers stay pretty steady since Washington doesn't get that cold and bodies are generating a lot of heat on the uphill & down that just need to be captured a bit more effectively. Occasionally the shell or even puffy comes on during the uphill if we need it, but that's only been at 9k on Shuksan in mid-winter temps or my partner's hut trip in Golden where it barely broke out of the negatives all week.
Jumping into your questions:
1.
Yes you need a down layer. Friends have assisted with a rescue 2 miles from the road at Kootenay Pass and got a major eye opener about how much time it takes and how cold everyone gets. The victim was in a guided class, and even with a lot of people moving her and her gear, it was a production just to get her to a lake as an open landing spot. Everyone got sweaty, and then everyone sat around for 2 hours. Midweight is the bare minimum. The OR Helium looks fine ~1lb and 800 fill, but has some of those weird hybrid vibes. The body is Pertex Diamond Fuse, which is serves a similar purpose as ripstop. It'll be durable, but it won't block wind any more than any other nylon woven. But the hood and shoulders have a medium-performance waterproof membrane. It's the layer I dreamt of when I wore my Cerium to work in the sun in the morning, but it started raining by the time I left. Standing on the summit of Adams, I'd rather go with the Rab Electron, which uses a very wind & water resistant Pertex Quantum Pro face fabric throughout the entire body of the puffy. It also is more oil resistant. Down needs to be clean to be lofty, but washing down breaks it down over time. My Rab uses Quantum products for both the outside and inside lining and usually makes it ~2 seasons before laundering compared to .5-1 for the rest of our basic down items. Or, if you're willing to slip on a shell when it's super blustery, go for the REI Magma. It uses 850 fill power so it's lighter and more packable than the Helium and still achieves the same warmth. It just uses Diamond Fuse throughout the body and knocks $60 off the price.
2.
No layering does not get as warm as a down jacket. I think a belay jacket is a great part to have in your quiver, but can probably wait til they get cheap in the spring and summer. It's a non-negotiable for me for my Rainier rope team, and if you do much travel to interior BC, it's essential. But a good midweight will probably be comfortable for 90-95% of your tours and keep you uncomfortably alive and health for the other 5-10%. Now, to explain how 1lb of a down jacket is warmer than the 3-4lbs of layers you used on Shasta. Down jackets trap air around your body. The puffier (either by fill weight or fill power) the jacket is, the more air around you it captures. Down is very low density. It's really similar to my fleece that I talked about in my resort kit. Warm air circulates freely between down clusters until you've got a nice warm air buffer between you and the cold. Now, the woven face fabrics or coated fabrics are a little plastic bag-y like a membrane. The Dawn Patrol is a woven and uses a Schoeller fabric, which tends to be wind resistant, but on the flip side, that lack of air-permeability means warm air from your body heat doesn't easily pass to the other layers. The Igniter has a membrane. The Dawn Patrol is almost completely windproof. And not to belabor the point, but one time I set up camp in a freezing, damp wind, and I jumped in the tent and just threw my puffy on on top of my shell. I wasn't warming up, and my friend was finally like "take your shell off, the puffy can't capture any body heat if it can't get past the membrane." And sure enough, I lost a layer yet got warmer. If you're trying to get warm, either layer very air-permeable layers (like a fleece, a Patagonia Nano Air or Arcteryx Proton, or a puffy with a skimpy, weight-weenie, ultralight face fabric) or just carry the warmer jacket.
3.
I don't get the current choice / potential option of active layers. Are you wearing any of these frequently while skinning? The First Light has 60gsm of Primaloft Silver insulation through most of the body (all but back, underarms, sides of torso). That's a warm jacket - lightweight puffies like the Nanopuff, Atom LT, or TNF Thermoball use 60gsm. The other parts of the hoodie are a 300 weight merino with nylon face. For $265 MSRP, they should be offering Primaloft Gold, and I don't love merino as an insulating material. It doesn't compress, it holds water, and all those wicking benefits it has in baselayer form are useless if it's not in contact with your skin, not on top of a base layer. If you're not skinning in this, just swap it for a down puffy that'll way as much, compress down to about the same size, and deliver a ton more warmth. I'd also skip the BD Vision Hybrid. It's also 60gsm of Primaloft Gold and won't deliver a significant increase in warmth over the jacket you already have. Are you looking at a warmer synthetic layer to replace the Igniter as an around town jacket? The softshell seems like the best choice for your uphill layer since it's a nice blend of breathability & wind resistance and the fabric's brushed on the inside for a little warmth, but you can definitely get that same combo for about half the weight.
4.
Does every pant in the quiver need to satisfy light & airy? You've got a softshell and a hybrid pant in your closet already. If you run quite warm, I'd continue to tour in one of those options. I assume you resort ski on a fairly frequent basis, so I just want to be sure you're intentional about getting another super light shell pant. The most breathable touring shells are also going to be skimming grams from other places, like the face fabric. A lot of the pants you listed aren't designed with weekly resort skiing in mind and might not have the longest lifespan used as such. To me, the bigger hole in your quiver is a versatile shell pant with the versatility to go inbounds and out and won't need replacing in 2 seasons. A few models come to mind with both inner & outer thigh vents if ventilation is a concern.
5.
I'd skip Stellar EQ. It's hard to spot vulnerabilities with shells over the internet, but there are a few red flags on other items. Like their tech tees use all overlocking seams, which leave that little flap of fabric on this inside that causes a lot of chafing. The Walmart tech tees that come 2 for $9 pays the upcharge for flatlock seams. But then they also weld and tape them like on the inside of a hardshell and laminate the hem. That's a ton of adhesives for a garment that sees a ton of laundering. If it were a good idea, someone else in the running market would be doing it. Or they have a 750 fill duck down puffy for $349. No special fabrics for durability & windproofing. No hydrophobic down treatment. The going rate for an 800 goose down jacket with some sort of Pertex face is $265.
6.
Definitely a more packable hardshell makes sense for spring; I'd also consider all-around alpine options. You'll get a 15-20% reduction in weight compared to the Mission for the shells on your list. Not sure on packability. I think a lightweight touring-focused ski jacket makes sense if you never plan on taking the Mission out to tour (even with all the space you'll free up in your pack dumping out all those extra midlayers), I think that's the route to go. But if you'd consider taking the Mission out for shorter winter tours, you could always consider an all-arounder alpine shell that'll be around half the weight & size for those spring trips where you really need to make room for crampons / harness / pro / overnight gear, etc.
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