I agree that ROTS was regarded as BY FAR the best of the prequels.

The problem is that the prequels were badly regarded, so it's like being in first place of the losers. Jedi on the other hand is in last place of the winners. Their review scores are actually not that different, but like I said, Jedi is in good company and is seen as a classic, while Sith is not. I think if there was no Episode I and II and Revenge of the Sith was released as a stand-alone prequel to the OT it would have been lumped in there the way Jedi sort of is, but such is not the case.