I agree with you on your points above, because Mourinho is a coach can cannot do without wey itu players and he knows the kind of players that he needs to become successful at the end of the season. When he did not ha ve those players he will not be able to perform well in that season. Assuming Manchester united gave him the players he needed, he would have done something great during his time in United.
It was the same thing Mourinho said in Roma that led to his sack because he asked for players but look at it now Roma is suffering from a big problem because their performance is declining since the last quarter of last season. Wrong decisions by a club management can make the club suffer for long.
Jose Mourinho knows how to win trophies. He doesn't need the club owners telling him how to do his job. The Glazers did not give Jose Mourinho the freedom to pick the players he wanted in the transfer market like other teams he managed in the past. I saw in one of his interviews where he was asked about signing Didier Drogba at Chelsea in 2004. Jose Mourinho told Roman Abramovich to pay and not speak. We all know how successful Drogba went on to become in the premier league and for Chelsea. This was Mourinho’s style and must rubbed club owners the wrong way. Clubs do not like a manager they cannot control and will look for any excuse to sack you.
With all the trophies and achievements that Jose Mourinho has won, he has publicly acknowledged that finishing 2nd place with that Manchester United squad in 2018-2019 was his biggest achievement. That speaks volumes about his challenges at the club.