I rather appreciate Kassadin having flash range on his r, because it's quite obnoxious dealing with bruiser level tankiness on assassin level mobility and damage.
And if the kit of the champion involves mobility around the map, plus damage on assassin level, plus survivability through mobility and free defensive stats, plus good cc, you literally have the same reasons why reksai and really, really old pantheon were nerfed: because you can do too much of everything to be balanced.
So fuck Kassadin, it was a long time coming. Patches upon patches of nerfs and he still remained viable, even on the high end of the power curve, so he deserves the nerfs.