That's a pretty bold claim. Most annoying sure, but outside of Lovie I don't know how to rank them. Frost is very unproven, even if we believe he's the best coach.
Fleck has a similar but less impressive resume - took a terrible-P5 team to an undefeated regular season, just took a a little longer. Rebuilding Western Michigan was definitely a bigger task than UCF though - prior to UCFs winless season they were good, there was some talent. WMU was not good.
Chryst was mediocre at Pittsburgh (understandable), and has been good at Wisconsin but no conference titles and had his worst year last year, when it's finally a team he built.
Fitz gets a lot of love because no one thinks you can win at NW, but it's tough to call him the best coach without winning a conference title in 13 years. I get that it's Northwestern, but I don't feel like he has a stronger argument than anyone else.
Ferentz and Dantonio both seem good but not great. They're definitely proven with actual conference titles. Iowa's was a long time ago though, and Dantonio followed up his 3 in 7 years by going 20-18 since then.
If you're going purely on resume, it's probably Dantonio - Ferentz - Fitzgerald - Frost/Fleck - Lovie. To be clear I don't think that's accurate, but ranking it any other way is subjective to some degree. It's really more incomplete grades for Frost and Fleck (and Lovie technically, but it seems pretty clear he's not good), they just don't have the time at P5 schools to know for sure. It's too early to tell, but I see nothing about Fitz/Ferentz/Chryst that makes me think they are definitely better coaches than Fleck.