send me a video of yourself skiing steep, icy bumps, a steep, icy groomer, and skied off woods with thin cover on prophet 90s and ill break it down and tell you every spot where youd benefit from a narrower waist. those 3 scenarios are pretty common in the east and more or less all mountain, since they avoid the more specialized areas of park, powder, and racing.
im not saying you cant ski them all over, im just saying youre doing yourself more harm than good by making it a one ski quiver. id much rather have, say, gotamas for pow, pipe cleaners for everyday, and a used, fairly short slalom race ski for hardpack/icy shitty days and for non-park skiing in general
if you have to have only one ski and you live in the east, it just makes more sense to go a little narrower in the waist- something like 80-85 in a twin. 90 is definitely fat when half the mountain half the season is snowless.