The key difference with the proposed system is that you can change how you're spec'd inside instances and so on with saved setups, so there won't be one "right" build. The "right" build for one specific boss won't be the same as another.
Now, you can say "THAT'S EVEN WORSE!!!" and maybe you're right, but I suspect the reality is that we will see more experimentation and more competing ideas on this. Sure most players won't be doing the experimenting, but that's never not been the case. The only game I can think of where even normal players did was Diablo 3, and this system is closer to D3's approach than anything we've seen before (and ultimately D3 required you to get specific sets to compete, and that made most choices invalid).
Wow, that's a pretty silly assumption.
Some of us have been playing MMOs a lot longer than any of the current WoW streamers, and were used to games which didn't have borrowed power. There's no doubt streamers popularized the specific term, but people disliking it is absolutely a real thing and predates the usage of the term.
You liking it is fine - it wasn't a total disaster - but equally not having it should be fine. We'll likely still get "new abilities every xpac", just as a new tier of talents (or even off to the sides or whatever).