It's not that people don't want mitigation/defensive utilities. It's just that those are not really necessary to survive anymore when you're geared enough, just like how early progression groups use vit melds, because otherwise they'd probably die. Back then the world first a8s clear team had their drg switch to mnk to help with the healing checks.

Once you're geared enough, those extra mitigation/defensive utilities don't matter unless they allow you to either cheese a mechanic (for more dps), or reduce the number of heals that need to be cast. Basically they're measured by how much extra healer/tank dps you can gain if you have those utilities.