Pelagos said specifically that they were no longer going to cast souls into the Maw and that the Maw, a hellscape for all eternity, was not an appropriate punishment in their afterlife.
Sylvanas has been given the almost impossible task of finding all the lost souls in the Maw and returning them to be judged and properly passed to one of the four domains. This is her near eternal punishment.
she has voiced her regrets because she was controlled (just like anduin recently). its not good or fresh story telling but she was literally sent to WoW hell for basically eternity. move on. its not like tyrande is doing much for her people except being a whiny emo (more bad writing)
Lets be real though. Blizzard staff constantly poops on Horde leadership and always have. Garrosh; Vol’jinn, Cairne, Saurfang now Sylvanus? Making Thrall a dirty hippie who cant be botherd to do anything when Azeroth is slowly dying.
I feel like the main reason they dont kill her off is cus if they the only leader left is gonna be Baine and hes a super pacifist cow.