Garrosh is interesting since his worldview directly follows from his life experience, ie the leader of a small community inevitably losing a war of slow attrition to the enemies who surround them. There is no negotiation, they won’t stop until you’re all dead, so the only rational response is to kill them all first.
Whereas Thrall, who grew up among humans, learned that, while he may dislike them as a whole, there are humans with whom negotiation and even cooperation to mutual benefit is possible (ie Jaina).
They were good foils for each other. For example, to Thrall the skirmishes in Ashenvale were nothing to start a war over: for Garrosh, this (basically ignoring a hostile entity) was insanity and he didn’t really grasp the value in it. It makes sense why Garrosh would go off the rails when his check was gone.
One of the less invoked crimes of WoD was retconning Garrosh’s arc in Cataclysm/Pandaland from one that naturally extended from his life experience to one driven by daddy issues- despite that arc being introduced and resolved in TBC. I’d love to read a behind-the-scenes tell all about the story development of WoW at that time period, it seems clear to me they didn’t go into Cata thinking Garrosh to be the villain of the next expac (the obvious buildup for that role went to Sylvanas).