Sure, we could call them barely sentient, but isn't that what the Alliance says about the Horde? So yes, it's a blatant tragedy. You can call Blue Dragons insignificant, but that's just showing your general disregard. And as for Ebon Blade members? That Ebon Blade member had agreed to work for Sylvanas, and no one really says her actions are justified or that she was right. Garrosh also started a war with Gilneas, that the Forsaken had no real need for. So that's another brilliant plan of his that backfired. If he'd had been given more control over it, as we saw in Sylvanas's visions, it'd have gone even worse.
And yes, I'd rather follow a Legion puppet. Blackhand knew how to hold his Horde together and reach out to other races and unite them. If Blackhand was ruling, I'd know a competent and cunning leader was in charge. One with a truly pragmatic mind, who was at least politically competent. Ideally, we'd all be working for Doomhammer, the most ideal Orcish Warchief we've ever had.
Sure, the Horde was being too passive about the incursions onto their land. No one disagreed with that notion. Sure, the Horde was in a bad place in regards to resources, but they apparently were able to get everything they needed to rebuild Orgrimmar quickly enough. I have no issue with some aggression. Garrosh simply managed to take it past the point where it needed to go.
So when you ask what he should have done? My answer is simply this. Less. He should have done a lot less. He doesn't need to launch an attack on the Alliance and throw away his defensive escort when he has more important priorities.
You can bitch and moan about how his people were suffering, but he rebuilt Orgrimmar out of metal, effectively turning it into one massive oven. He had his secret police terrorizing his citizens into obedience by the time of Theramore.
Maybe Sylvanas isn't any better. Maybe she's worse. Maybe comparing Garrosh to Sylvanas doesn't do anything to make him look good.