All good points so far, though I'll add my two:

1) In Legion, there are no buffs. Most classes have some 2-3 minute cooldown utility ability, but otherwise you don't have to have a specific mix of classes to attain all of the appropriate group buffs. This pretty strongly incentivizes stacking the same class if possible.

2) It is pretty easy in ISBoxer to manage the DPS/tanking rotation of any class that is resource limited or first-come first-serve (FCFS) style. For instance, it's pretty easy to setup an optimal rotation for Hunters, EShaman, Warriors, Death Knights, Demon Hunters, and RPallies. I would say you can get 90+% efficiency on those classes. Mostly, you're figuring out how to maximize big cooldowns.