This guy ran 1/8th of the distance of his specialty in an Olympic trials qualifying time! Take any of the best Americans and ask how fast do you think they can go at 1/8th of their specialty distance. When you do this, most of them have PRs in those 1/8th distances which are worse than the Olympic trials qualifying standards in that distance. This suggests that Jim Walmsley is better at ULTRAs than the following athletes are at 10K
Shadrack Kipchirchir (3rd all-time 10K for USA - US Olympian 2016) - 1500 PR = 3:49
Sam Chelenga (4th all-time, 6th at Olympic Trials 10K) - 1500 PR = 3:47
Leonard Korir (10K - US Olympian 2016) - 1500 PR = 3:44
Scott Fauble (4th Olympic trials 10k) - 1500 PR = 3:46
Chris Derrick (5th Olympic trials 10K) - 1500 PR = 3:39
With the exception of Rupp, Solinsky, & Jenkins I don't think any of the recent great American 10k runners have achieved the 1500m Olympic trials standard of 3:38 from what I can tell. A similar analysis would hold for the women, very few of the great American female 10k runners have 1500m PRs below 4:09.
Now if you took some of the best Africans in the world, they might crush this guy, but definitely not most of the best Americans. This guy is actually pretty darn good.