You make a good case but I just can't get on board with this. Lets challenge this a little.
1) Real Madrid. Had one of the best squads in the world, may have scored goals and points but won nothing. It wasn't due to Mourinho, he was sacked because he failed.
2) Malaga. Did a good job, but had lots of money to spend. Again didn't win anything.
3) Villareal. A truly outstanding job but it was over 10 years ago now.
4) City. Won 1 league title in 3 years in a period when the top teams have been in turmoil. United have struggled, Chelsea have struggled. Champions league record of 1 semi final and two group stage exits, given their resource is very poor.
The season he won the league I would say it was more handed to them.
All of the above indicated a downward trajectory to me. His defence looks all over rt. place to me given the money he's spent. He remains very reliant on players Mancini bought (i.e. Silva, Company, Aguero & Toure).
Finally age is important in all of this. We are in more of a mess than we like to think. It's recoverable but he is an older man now. I think we need to get a manager who can be here potentially longer term and take a couple of years to sought the mess out.
I also feel as a football club our strengths are not suited to a Pellgrini type manager. Even with Moshiri's money I am doubtful we will be eating off the top table. Our strength has been an adept scouting system and strong youth academy. He will not maximise them.
If you compare his record to De Boers it does not stand up. Compare his record at City and Real Madrid to De Boers in Ajax (both at similar size clubs in terms of spending compared to the rest of the league). De Boer won 3 titles in a row, Pellegrini scraped over the line once in 4 years.
Bought Joaquim when he was 30 for 2.5m for Malaga
Bought Toulalan for 7m when he was 27 for Malaga
Bought Monreal when he was 25 for 4m for Malaga
Brought an 18yo Cazorla up from the academy into the Villareal team
Bought a 21 yo camacho for Malaga from Althletico for 1m
Bought a 19yo Isco from valancia for 2.5m
Signed Rodriguez for Villareal from river for a nominal fee, was a starter at cb for that villareal CL team that knocked us out at the age of 20
Bought Riquelme from Barca having loaned him for two seasons for 6m at Villareal
Bought Forlan from United for 2m - a player who have been labelled a huge bust for his time at United, 1st seaosn at Villareal he won the spanish top scorer and european golden boot
Bought Senna for 400k - as someone who still played in Brazil at 26 - that was an amazing purchase
Honestly mate thats just going through a couple of lists of the malaga and vilalreal teams he put togetehr, anyone with any doubt he can't operate and find great talent without having real madrid like money doesnt understand his history and some of the players he has turned into stars from busts at other teams
On a comparative note though, everyone is clamouring for Mourinho - and Pelligrini in the last 3 seasons in the prem has outperformed Mourinho mate