If you look at the achievements of United after the dismissal of Mourinho (in 4 years 0 titles with a stronger squad), then I would not say that his work there was unsuccessful, everyone just got used to a much higher bar in his performance. Tottenham, he also initially raised almost from the bottom of the standings. Mourinho is a strong coach and now he has some opportunities at Roma (I don't think it's about scudetto) and I hope he can use them.
I do not know
I don't agree very much, I don't judge Mourinho well as a coach
but maybe I am wrong, since I am not competent in the matter
why do you think he's a good coach?
I have seen others, in my opinion, better than him
A very strange question - you can just look at the Wikipedia page with a list of his achievements, well, it makes no sense to breed offtopic here. Going back to Serie A, which clubs have won the European trophy in recent years? This is Roma (under Mourinho), and before that, 12 years ago, Inter won the Champions League (and also under Mourinho). Coincidence? I don't think so