I disagree with your reasoning. All because Pellegrino never had the support that Mourinho has been getting for the last 3 years. Pellegrino's Madrid never had € 300 millions to spend on players that he barely uses. But still his team used to play "a la Madrid" style, offensive,attractive and effective. And Pellegrini lost the championship to Barca not by much unlike Mourinho. And Barca at the time were well rounded team with no deficiencies like the past 2 seasons.
Mourinho is a type of mercenary to get the job done. Don't ask him to play an attractive soccer or develop young talents. It's been like that since his Benfica days.
He is a good psychologist but not a player developer.
Do you know if Mourinho is in charge of transfers? I would suggest he isn't as that is becoming less and less common these days, but he still made a huge amount of progress
He very definitely does develop players, there is a reason that so many players are so loyal to him, he just makes them into better players, see Frank Lampard.