For all the posts people do comparing this to Garrosh, there are enormous differences:
Garrosh started out with an event where he actually killed off one of the racial leaders (Cairne - even if it WAS Magatha’s fault, that’s still a massive point to start out on).
Sylvanas came to power after she carried Vol’jin out of the Broken Shore and helped the Horde withdraw without losing its remaining leadership.
Garrosh took the affirmative step of letting the trolls, blood elves and forsaken know that he loathed them and considered them worthless or corrupt.
Garrosh actually took the step of trying to assassinate the leader of the trolls. (Vol’jin was chief of the Darkspear, while Saurfang was never the chief of the orcs, let alone even one of the orc clans). The Horde’s rebels did not consider Garrosh a “tyrant” because he played hard-ball with the Alliance. They turned against him because he literally sought to subordinate and dominate various non-orc parts of the Horde to the orcs.
From the bird’s eye view of storytelling, Sylvanas does not care for the Horde’s people, but at the ground level, she’s flattering and diplomatic to the various races. Garrosh was open about his loathing.
In keeping with that, another important difference - Garrosh SHRUNK the Horde’s constituent parts. Sylvanas has ADDED to the Horde’s constituent parts - Highmountain, the Nightborne, and the Zandalari are all groups brought into the Horde’s fold on Sylvanas’s orders.
Resources - Garrosh wanted resources to go to Orc prosperity, and in the game and in tie-in materials, this was a pretty big goal of Garrosh during the war. (They even had Nazgrim, when he died as a loyalist in MoP, refer to the desire for prosperity as he died).
Sylvanas and the Forsaken, on the other hand, are kind of dissociated from a need for “prosperity” in any traditional sense. They’re undead, they don’t need good food and housing. They are much more focused on destruction of the Alliance, whom they see as a threat to their existence, as a goal to secure a permanent safety for the Horde (mainly themselves). There is not a sense of the Forsaken trying to subordinate the other Horde races - they’re just focused on destroying Alliance power, which isn’t really something that stirs up the other Horde races in opposition.
Long-story short, the difference between Sylvanas and Garrosh is significant, and it’s really silly to try and paint Sylvanas as Garrosh 2.0 or BFA as a re-run of MoP. It’s a comparison that only works at a very shallow glance.