A common, and misleading, explanation for Minnesota's success pre-62 and the decline after that.
From Wiki: "George Henry Jewett II (April 1870 – August 12, 1908) was an American athlete who became the first African-American football player at both the University of Michigan and Northwestern University, and in the Big Ten Conference. He played for the Michigan Wolverines as a fullback, halfback, and field goal kicker in 1890 and 1892 and was considered one of Michigan's greatest players in the pre-Fielding H. Yost era."
The whole Big Ten enjoyed the benefit of players of all races throughout the 60s as many schools and some conferences remained whites-only until the 70s.
The bigger, and unique, reason the Gophers lost their recruiting advantage was the arrival of pro sports (especially the Vikings) to the TCs in 61 dislodging the Gophers as the premier Minnesota sports attraction. Blue chip players chose schools like Iowa and Wisconsin which don't play in the shadow of the NFL.
Besides the the Gophers' subordinate place in fan and media adoration, other recruiting disadvantages include limited in-state talent, cold weather, distance from talent-rich areas, a non-college-town atmosphere, and the decades-long history of poor-to-mediocre performance.
The Fleck and Mason eras lifted the program to above average performance and they deserve credit for doing so given these recruiting disadvantages.
What is the ceiling? I don't know, but I suspect 2019 is pretty close to it.