Well, it was only the defence position (and potions) that was terrible, everything else was fine. Also care for magical creatures wasn't great as well I guess. He had no choice but to keep Snape in potions, and as for defence there was nothing he could do, the job was jinxed. He did hire great teachers, Lupin, Barty Crouch Jr, even Snape.

The only questionable choice he made was Lockhart. He had no part in Umbridge's employment and as for Snape while he was unpleasant he was a competent teacher. We have no mention of how Quirell taught so I won't include him here.