I won't deny that Sylvanas has a presence even if she rarely appears and while that's ordinarily good, it's something Garrosh also did, but in a more meaningful way. We saw the worm's eye view a lot more in Mists, with how your average dude was doing, thinking and was treated. The individual racial leaders were likewise characterized in more detail. Gallywix's story is a standout, but so is that one with the Dragonmaw orc. I won't vouch for all these stories, I definitely wouldn't vouch for Mists, but it objectively better executed and better handled the effects of its designated bad guy's reign.
I agree with the differences you've voiced re: Garrosh, though Mists was quick to sweep them under the rug. With Sylvanas, I'm taking it for granted that her thought process in Before the Storm was tricking the reader, since her goals there are extremely basic - destroy Stormwind, raise the population, divide its lands among the Horde. That version of Sylvanas does want the Horde to win, even if it's not a Horde many would sign up to and raising a city's worth of people is something of a dick move. A Good War muddles the water somewhat with allusions to her true goal and in-game it's anyone's guess what she's doing and why. I'd be pleasantly surprised if they stuck with her doing all that to destroy Stormwind but I really doubt it.