Mourinho is very good at getting the most out of a team. But he is not good at building a team. That is why he was awful for us and perfect for Spurs.
I really disagree with this.
In Leiria he got many players together and reached 4th in the league, the club's best position, while doing things such as winning away in Benfica 0-2.
Porto was in a really bad place when he came mid season, he scrapped to reach 3rd place to get Europa League. He basically bought half the Leiria team (Porto could do that) and together with other players he mounted that amazing Porto team that won the UEFA Cup and, incredibly, the Champions League. That was the last time a club outside the top4 countries won the competition as the monetary difference keeps spiralling out of control.
He went to Chelsea that had a good run before with Ranieri, he of course had almost unlimited funds but he bought well and joined together players that would be successful for the club for 10 years.
I think Abramovic fired him because he thought with that super team anyone would win - and as it could be seen it wasn't that simple. And his team in that year reached the final with Grant just somehow being there.
In Inter he was the telegraphed champion of Italy but they were underdogs in Europe, he sold his best player (Ibrahimovic) in order to have enough money to buy all the players for positions he needed. The players here were experienced and not thinking about the future but leaving the club with the only squad in history that won the treble in Italy (including beating super Barça) is nowhere near bad.
He then went to Real that were minnows vs that super Barça and in Europe too (7 years eliminated in a row in the round of 16!).
The team already had great players like Ronaldo but it was just not able to stop being eliminated by Barça, like he was in the first game.
He was able to get more players to this and turned the tables vs Barça, so that in the end of his run Barça was unable to beat Real directly, while he got to 3 semis in the CL in a row, losing in the second year to penalties.
In this 3rd year things went bad, we will need more years to know what really happened, but it seems some players reached the limit with him, most likely Ramos and Casillas as we have heard/seen, but why exactly this fallout happened I don't know.
Still Real Madrid was left in a much much better position than when he came, winning the copa del rey 18 years later (this one was more of a token victory vs that super Barça), then winning the spanish league with the points and goals record (even above super Barça), and he did this while spending less in his 3 years combined than the year before him or the year after alone.
He came to Chelsea that was a top 4 team at the moment and in the first year he finished 3rd in the league and the semis in the CL, having won all 4 games vs the team above him in the league. And his strikers were an almost retired Etoo, Ba and post-liverpool Torres. In the second here he got 2 or 3 key players and won the league.
Again in his 3rd year right at the beginning things went super sour, with that Eva affair, and even later after the court case closed Mou still didn't want to apologise to her. Was he a super twat simply? Was there something else related or not to her? Again it will be very interesting to check in 10 or 20 years what really happened. Things went bad and he was fired, months after being champion.
Then he went to Man Utd, that was in a dire situation. I think Mou thought Man Utd had a solid football structure in place and imho he got shocked that there wasn't none. He scrapped to win trophies with that team (no, Lingard shouldn't play more, Redcafe ffs) and even reached 2nd in his second year, but the team wasn't good enough. DId he want the players he bought? I don't know. But I think he was very unhappy how the club was run in the inside and basically got bitter over his frustration. The team slightly improved imho but not enough, so that it keeps being a team fighting for a top 4 place just like recently.
Ok I wrote more than I wanted, but basically what I mean is that in all his runs the club was better than when he left - with the momentary (not global) exception of his second Chelsea stint and Man Utd.