Mages have cloth with no armor increases like priests and locks so they have the least armor.
2 ice blocks, cautrize, and greater invis are all on the same tier so you only get 1. Normal invis is only really used on openers not much for surv.
Ice barrier is ok but easily purgable, against any shaman team its non-existant.
Alter time sure, however usually used offensivly.
You shouldve mentioned spellsteal as thats usually the best pure survivability they have is stealing hots and shields.
I define squishiest are that which takes the most damage when you hit it. Mages ARE the squishiest class in game.
OT: Blink isnt that OP tbh, im so used to it that it seems natural. I would count lock port as being the most OP, rediculously strong on certain maps, with proper positioning you guarantee LOS pretty much on demand, and now you can give it to druids.