Only drill I have had in a lesson that was memorably terrible was dolphin turns. Really painful for my toes and one I will flat refuse to do. I'm sure I was doing it wrong, but no advice was offered. Only saw it in one lesson and glad to have not seen it again. Evidently I am not good enough to do this without pain.
The 'drills' I find to be a 'groan' lately are the static demos. One being 'stand on this mound here with your ski tip/tail free and see how you can pivot the ski from the hip socket.' Another is the 'edge tipping and angulation while the instructor tries to pull you downhill.' Thankfully I have not seen these in a while, but sometimes they come up in group lessons, and with a big group and demo on every member...
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I am sure there were many other drills over the years that were hopeless when I had rental ski boots, but we soldiered on anyway.
The proper drill done poorly is not helpful. It could make things worse if practiced poorly outside the lesson.