Problem is, since every content can be accessed by a random party setup, you can't design content where one tank job can't MT. So, if all tanks can be good MT, all tanks should be good OT too.
Well, right now, we have 3 tanks, and 2 clearly superior combinations. Create another OT (Still viable as an MT), and you'll probably end with only 1 superior combination.
Frankly, I really don't look forward to a 4th tank...In fact, I wonder how many tanks other MMO managed to do without clear overlapping or serious balance issue.
