Ice is pretty easy to fix, type matchup-wise: give it a couple of extra resistances and lose one of the weaknesses. I suggest giving it resistances to Dragon and Water and removing the weakness to Rock (both because it doesn't make sense, given that ice cracks rocks irl, and because of my well-established dislike of Stealth Rock screwing over everything weak to Rock). Maybe even go the extra mile and make it resist Rock in place of the weakness.However the problems many types still have remain such with Ice and Dark. These types either need a Type boon to make them further useful or new types which are weak to/resisted by them.
I mean, you'd still have to get Gamefreak to stop making every Ice-type slow and bulky, but at least it wouldn't be the single worst defensive type in the game any more.