I didn't say he was the greatest of all time, just that he was a better coach that Mostert. In the same way you could argue Kipchoge is the greatest marathoner ever, but Kiptum was better and just didn't have time to rack up the accolades.
I'd argue that the fact that NP turned around so fast after the joined, and it fell apart so quickly once he left, was due to his coaching abilities. I don't think the Youngs or Sahlmans are Fernandez/Nuguse/Kessler level talents. Pretty far from it, in fact. I think there are dozens of Young/Sahlman level talents running track every year, and most of them just don't get the coaching to reach their potential. As evidence, we can compare L&L to Nico. In March of his freshman year, Nico was 4th at NCAA XC, and in April ran 13:24 to run a U20 record. As of March/April of their freshman year, L&L are pretty far off their HS PBs, much less scoring at NCAAs. Leo did recently run 7:54, but given that Lex ran 7:57 as a junior, and Leo was significantly better than him all year, I don't think it's too impressive. I think they still have the potential to win titles before they graduate, but if they truly were massive talents, I think they'd be running better.
And I'm glad you brought up Soles, because I'd like to use him as my 2nd piece of evidence. He took over Herriman a few years ago, and he's already pumped out an 8:43 guy, and had 3 other guys run sub-9 yesterday. I think he is proof that a coach can show up and turn a bad team into a national title contender within a few years. He did it a bit faster than Brosnan (admittedly coming into a better program, and having far more experience), but the numbers line up pretty well with NP if you take out the Youngs and Sahlmans. 8:43 Jenkins to 8:44 Aschbrenner, then 8:57/8:58/8:59 to 8:52/9:00/9:02. They also both have around 2k students. Tbf that's 6 years for Brosnan vs 3-4 for Soles, but Soles gets the altitude advantage, and Brosnan gets the unique disadvantage of not getting to count his top 5 best athletes.
I think if you put Brosnan or Soles at any school that's comparable in size and wealth to NP/Herriman, they'd be contending for national titles within 5 years. I'll also go ahead and predict that Soles is gonna have at least a couple guys run similar times to NP's best in the next 5 years.
Also Cantu technically did run 8:57 while Brosnan was coaching, but it was Sean's wife. I took for granted that that meant Sean was writing workouts and stuff, but if you don't want to give him credit for that, that's reasonable. I don't think it's fair for you to say I'm ridiculous for giving it to him, though.