If you look at how the specs perform throughout Legion so far, you can see that there isn't a single class where the differences between specs were at least somewhat consistent. The problem is not that one spec is performing slightly better after changes, it is that it performs way better:
Mage: Fire was god at start, but now it's horrible, so mages are pretty much forced to change to frost.
Hunter: MM was the go-to, now it looks like BM is stronger.
Warrior: Arms at start, Fury now.
Death Knight: Unholy then Frost.
Warlock: Demo/Destro at start, Affliction now, and it seems like it will go back to Destro if nothing changes until 7.2.5 launch.
Rogue: I am not 100% sure about rogues, but I think at start Outlaw was the best, and now it's Assassination.
It's needless to say that someone should play what they want and like, but it's normal for someone to want and like to perform the best they can. So if someone wants to do that, they will have to switch specs, no matter their preference.
What are your thoughts?