Yeah, he didn't seem much stable either. Wrathion fucking sucks at choosing allies.
Not if the charismatic orc is manipulated as well. Blackhand was doing "fine" as long Gul'dan didn't fall into coma.
I would say Garrosh could have worked decently as "rallier" but he was definitely too unstable and unpredictable to be properly manipulated. In fact I think that, right after creating the Iron Horde on AU Draenor, a new orc among them should have been found, someone more stable and like-minded, to do the same trick on all the other Hordes. Once you got someone like that, Garrosh should have been killed for good. However, Kairoz failed way too soon by getting himself killed by a fucking Garrosh with handcuffs.