Both started a war.
Garrosh dropped a manabomb on Theramore.
Sylvanas burned down Teldrassil.
Both managed to bring up, not only the Alliance against them, but also their own people inside of the Horde because of how atrocious these acts were.
Garrosh tried to have Vol'jin assassinated
Sylvanas tried to have Saurfang and Thrall assassinated, and Baine executed.
Garrosh brought both the Horde and Alliance together to raid Orgrimmar and defeat him.
Sylvanas brought both the Horde and Alliance together to a showdown in front of Orgrimmar, until she had to flee.
Garrosh escaped his trial.
Garrosh and Grom confronted Mannoroth in an epic cinematic.
Sylvanas confronted Bolvar in a cinematic.
Garrosh basically was the catalyst for the events of WoD, linking our world to that of a Draenor from a different time and opening a portal.
Sylvanas basically was the catalyst for the events of Shadowlands, opening a portal to the Shadowlands.
Both waited for us in the new "world" that they fled to.
Only difference is, Garrosh was a good character.
edit:
It gets even better when you think about it.
Garrosh in the WoD cinematic, Gul'dan on the ground.
"This was not our destiny."
"Times change."
Sylvanas in the Shadowlands cinematic, Bolvar on the ground.
"That power will be your prison."
"This world is a prison."
That moment reminded me a lot of that moment in the WoD cinematic.