I mean, let's face it, his team is also not that great. Do you think most of Atletico's lineup would be starters in Barca or Real? It's a genuine question.
Sure, he got a very hefty lead at some point, but you can also argue that he got that lead by getting his team to overperform, which is not necessarily sustainable on the long run, even with a great coach. That being said, I don't think he's in the same league as the best managers around, but what he did for Atletico is still pretty amazing to me, overall.