If people didn't see, subcreation put up a historical list of class tiers for M+ going back to when he started it, BFA S2. So 6 seasons of data, with the current tier pretty much going to map onto the previous season.
https://twitter.com/subcreation/stat...54407534399488
Given the way the rankings work I think it is legit to quibble around the margins about accuracy, but in the broad, macro picture this pretty much maps onto what everyone already knows. Basically, Melee in m+ is completely dominated by the 3 leather classes, with the plate classes and others usually ranging from mediocre to bad every single season.
Ranged sees much more variance, where even consistency good specs like elemental are worse overall than the leather melee train.
Thankfully, it does seem like the DF talents should help out healers and tanks the most, since a lot of those rankings are based on DPS which the developers didn't even seem to bother to try and balance until recently (and it's still not great).