Absolutely. My RoM is really actually quite bad in hips, back is tight enough that it's restrictive. I'm plenty strong (and will continue to do strength training for health/wellness) but continuing to focus on strength for skiing in the offseason is a mistake--lots of room for stretching, RoM, and proprioception work this summer. I don't think I've quite "thrown away" previous off-seasons, in that I've set up a good fitness base, but to get serious about skiing I need to bring my flexibility and proprioception from "bad" and "below average" to "above average", not get strength from "quite good" to "quite good plus 3% better".Don't forget to work on range of motion... lots of skiers have none, and yes, you need it.
I've got a booking with a physiotherapist who has done work with ski teams, and is a skier himself, next week, so we'll see what he has to say and recommend early next week.