I think this is correct. UM is not a job for a first time HC, especially when it's a program that has been down for almost two decades. He needed to learn how to be a HC at a school like Temple where he wouldn't have such a spotlight on him. I think he did some good things at UM. Haters want to downplay his decision to go from pro-style to a spread offense and say it was the obvious move. It wasn't obvious enough for every coach before that or even Mark Richt.
He wasn't an ace recruiter, but he doesn't personally have to be if he surrounds himself with recruiters. I think he recognized his recruiting needed to improve which is why he brought in recruiters like T-Rob and tried to get Travis Williams for LB coach (I think he hired him but T-Will took another job shortly thereafter).
He also managed to bring in one of the best dual threat QBs in the country coming off one of the worst offensive season under Enos. And he turned 3 star Rosseau, who other programs were looking at as a WR or Safety, into a 1st round pick at DE. Fans are rightfully lauding Cristobal for finding 4 star Bain who is a 5 star, but Diaz did something similar. And Diaz convinced Jalen Phillips (who was medically retired from college football) to give it another go - and he also became a first round pick. So he wasnt too bad at landing DEs.
Ultimately he shouldn't have been hired in the first place, but he was. Didn't work out, but I think you have to be a real salty ***** to hate on a first time HC for making rookie mistakes.