Know what would happen? A mass exodus of tanks in the game. They'd all roll DPS or possibly healer, or just straight up quit the game. In my opinion, the reason why we see tank dmg (DRK and War in particular) increasing is the same reason why Tank damage increased in WoW (a prime inspiration for FFXIV) and other MMO's, Doing damage is "fun". Granted, it's not the main job of the tank to focus "solely" on damage, but knowing you're contributing actual damage while being a tank makes the role more fun more *most* players (there are those weirdos (j/k) that don't care about dmg). I think people are still stuck in the early to mid 2000's when tanks were low damage meatshields. Times have changed since 2004/2005, tank classes were always hard to fill in groups, increasing dps/dmg helped alleviate that.

Now, as for the str v vit thing. Until SE gives encounters that actually *REQUIRE* full vit, you're going to see more str based tanks. It's quite possible that this is the design all along (with vit stacking for the "progression" encounters like savage).