It's probably a bit harsh but I think he failed at Bayern. Not winning the CL is one thing, not reaching a final however, is pretty damn poor. And yeah, he won the league, but I think that was the bare minimum given the circumstances. Spend way more than their only league competitor. Got both their best players in a short space of time. And like it or not, he took over a side that had done what he could not. When you have the resources bayern do, you can't really use injuries as an excuse. Though, apparently he didn't have full say over transfers, but still, look at the squad he had.
He's judged by ridiculously high standards now. But if you're being argued as one of the best managers of all time, then that's what happens.