It's not really about armor though. Armor is not a problem near the end of the game, as magic is a far bigger concern. Adding some magic armor + shield up is way more useful than all the heavy armor money can buy. In fact, I've even found myself grabbing a few points in int so I could wear robes on my "tanks", as I suddenly realized my wand + shield wearing casters were getting tankier than my heavy hitters.
That being said, for a "tank" I'd probably just get enough strength to wear stuff and then go int + magic anyway, while still maintaining all the useful knock downs, movement abilities, shield up, deflection, etc stuff that tanks get.
