I think they need to be aiming for within 10% in all content. In raids there seems to be some cover with the fights being different enough that most specs will have their boss. But M+ is just different degrees of the same damage profile.
There’s this ( link below ), and I did one for 9.1.0 as well. One thing you see is survival moving from 17th, to 10th, and I’m guessing it will be first or second this tier.
This raises the suspicion that they’re intentionally using balance for goals other than balance. It’s not that they can’t balance things, it just they have misguided goals other than balance.