the tanks tend to still need to pay attention to when to use their mitigations right so the healers can do this in Savage content.

Yes, but this is core to tanking. It's not an extra thing that only good tanks do, it's a fundamental aspect of the role. You more responsible for mitigations than any other role (even healers like WHM have less mitigation options than any of the tanks).

It's as important as using personal mitigations on tankbusters. You mitigate raidwides. A tank that does not use all the mitigation options available to them is a bad tank.

This is to say, why should the job that is doing less the more everyone else gets better deal more DPS than the rest who has more to juggle to reach that point?

Healers aren't doing less than others though, and even if they were what they do is different from the others, not lesser.