I'm of the camp that thinks tanks should be on par with melee damage... however they should only be able to achieve that BY tanking so you can't just stack tanks. Cover/Counter and other tanking mechanics have been some of the highest damage options traditionally in final fantasy games, and many other games have hit this balance of dishing damage while recieving damage perfectly (xenoblade series hits this very well, with the tank characters being often your strongest damage dealers, but needed to retain aggro or forward positionals to achieve that damage). The issue with FFXIV is the presence of an Off tank in all 8 man duties, if tanks had to work as a tank for their damage, the off tank would be stuck with nothing to do for most fights.