I feel like I've found Yeti marginally easier than Santa so far (plug with lots of snailbites, and then he's actually vulnerable whilst rolling), though it's hard to tell because so much is just the luck of what state I'm in by that point in the game - Snowman I feel is definitely the hardest of the three, but that's partly because I haven't found good tactics for him yet. That present change would make the Santa harder, certainly, might be interesting to test at least. Why did you change the minions to ice mages, btw? I can see the logic behind making them tougher, but I feel like using that many ice mages specifically may make the boss fight excessively tough in runs where you don't find a mammoth amulet... I dunno. I just have a feeling that with three Ice Mages + trying to fight a boss, I'll just end up using scrolls or fancy one-hitter tricks any times when I don't have that amulet and would never actually do the fight properly.
Also, minor point - if I'm right from observation, the rocks in the long jump rooms currently never have items in. This seems kind of unfair, as there's no way for players to tell that they're not normal rocks.