One season is hardly enough to judge Mourinho's ability as a manager. So he was on a rut at Chelsea last year, so what? He's suddenly an ineffective manager now? That kind of thinking is too simplistic.
I believe it is more than one season to judge mourinho. His overall performance with chelsea is not really impressive, he won with some luck and most of the time he relly alot on defensive strategy which makes chelsea an extremely boring team to watch. I doubt he will be able to bring glory back to manchester united
Then why did Manchester United hire him? The Man United board of directors deliberated on hiring Mourinho or not for months before finally deciding to get him as manager. Why? Because of his ability to win trophies.
He has had an impressive career. His trophies and record speak for itself.
https://en.m.wikipedia.org/wiki/José_Mourinho