Salary should only be used to measure what it took to get him to come there at the time, not how successful he’ll be compared to others. People do this with Kirk Cousins and Andrew Wiggins all the time. Yeah, if you look at them and all you see is the 3 year 84 million dollar contract or 29 million a year super max contract a year then yeah, you’ll be disappointed.
If you don’t let their salary influence your expectations for them then you can appreciate them for they are and what fair expectations for them should be. Just because the Vikings made Cousins a top 5 or top 3 highest paid QB's in the league at the time doesn't mean you should expect him to perform as a top 5 QB in the league. All it means is that was what it took to outbid the Jets.
Just because Michigan pays their coach a top 4 salary in the country, doesn't necessarily mean being the #4 team in the country is a fair expectation, it takes more than just throwing money at a coach and facilities to have a top 4 program.
If the gophers were to throw $15 or 20 million a year at Saban, Urban or Dabo and they came here, that doesn't mean being #1 in the country and winning a national title is a fair expectation for them at the U. All it would mean it that was what it took to pry them away from their previous stop.
If you have two options and one is to pay a coach $8 million but is only worth $6 million, or you can pay a coach $3 million and he is worth all of $3 million, as long as I have money to spend which Michigan does, I'd rather overpay by $2 million and get the coach worth $6 million than pay $3 million and get the $3 million coach.