Garrosh has never been 'good', but he was still honourable. Even in Wolfheart, he valued honor in battle, and he even valued the Night Elves as honourable opponents. So yes, you're right that he's usually portrayed as a warmonger, but he was not a monster who resorted to underhanded tactics like murder and hurting innocents. This change came with MoP, and most likely because he was decided to become the big bad of the expansion.