As it stands it's "Optimal for my class", with Shadowlands it will be "Optimal for class and my convenant", not just the latter.
Classes and covenants are not the same, there can be two classes with differing covenants and one will start from a more optimal position in any given content than another. Does it mean they will end up in the same place as they start? Maybe not, but to equate the two as the same thing isn't true. Even to the point that you can change your covenant (with limitations, penalties and hamstrings) but I can't change my class on a character.
The covenants are meant to be a rewarding, empowering choice, but to some (possibly the minority, but that doesn't negate their opinion) they actually feel like a hindrance in other forms of content they previously were able to optimise for.
Sure I can optimise my class in SL for Raiding with my covenant choice, maybe even make myself passable at M+ with a few conduit swaps and different soulbind, but I won't be as optimal as the SAME class with a different covenant.
I don't know if this has ever happened in the game before?