(Mildly Interesting) In the Trial of the Crusader Raid, they updated Garrosh's model but not Thrall's.

This is most likely because Thrall was still wearing the Doomhammer Plate set at the time of these events. Remember, it wasn't until after he quit being warchief that he put the armor away and donned a new hippie-robe. Garrosh on the other hand, has not changed his appearance lore-wise, so his model makes sense to have here.

It would break lore, i suppose. Hoodie thrall is the Earthen Ring thrall. Current Garrosh, i guess, is a retconned model. Can't explain the hold and outland model. Guess devs are just lazy or it's not a high priority task. But then why just replace only the ToC model? The "lazy" bit seems more plausible here.