I think people are really jumping the gun on this.

We basically have to wait until 8.1 Savage to actually see how the difference between Main and Off Tanks is.

Even once we get the full list of job actions for every tank, we won't get to really experience how it plays out until we get higher end content to mess around with.

They've already expressed wanting healers to focus on healing and for the bosses to be more active. There's a good chance that the damage profiles in high end encounters becomes completely different from what we're used to.