Enmity generation has never had anything to do with player skill outside of snap aggro, which was a pass-fail check. If you want to differentiate between tanks, you need a positioning/movement check. Even small repositioning checks produce large variations in player execution.

Mitigation and damage normally intersect anyways, because plenty of mechanics are designed to coincide with burst, adding in extra weaves during your damage window. It would likely be more obvious without a one button burst design. Historically it was done by coupling resources to mitigation, like Raw Intuition and Vengeance generating Wrath/Abandon stacks, or by giving tanks proc-based counters like Reprisal and Shield Swipe. Both of these options are open from a design standpoint.