Gameplay needs to be the bottom line.

Enmity matters most when you're establishing aggro on a mob. You want enmity to matter? Throw in lots of adds, have them make a beeline for the squishies, and get your tanks to intercept them before they oneshot them into oblivion. That has a lot more gameplay value than choosing between combo 1 and combo 2 every X combos.

Even if it's something as simple as enabling crit-autos on non-tanks, the risk of having an untanked mob oneshot your team is what gives enmity value. Without it, it lacks meaning.