I didn't listen to the podcast, but obviously I know Rojo and Wejo (and the other guys a bit).
If that's what they talked about - then they bring up some good points actually.
First off all, UTMB is generally "deeper" than most ultras because of the sheer numbers. You've got like 3000 runners just in UTMB (many international too)... Compared to WS100 or Hardrock where it's less than 400 or 200 runners (or some other "small" US ultra). FYI "golden ticket races" refer just to the ones for elite entry into WS.....not UTMB.
I'm not aware of very many sub 2:10 marathoners that have done UTMB, but to not think Marathon time matters (or is highly correlated with ultra performance) would be silly.
Jim alone is a 2:14 guy...if he had focused on the roads he probably could be sub 2:12. Zach, might not have been able to ever crack 2:20 though. I don't know, maybe he could run sub 2:18 though.....I'm sure he would be at least sub 2:24. But generally they are going to destroy any 2:35 + or 2:40 guy at UTMB. Sometimes the 2:25 guy beats the 2:15 guy, but generally the faster you are at the marathon, the better your ultra is going to be (even on a real mountain course like UTMB). Keep in mind UTMB is not really a "technical trail" also.
So in theory if a bunch of East Africans who were sub 2:10 guys actually got into UTMB and had the gear and trained for the mountains a bit, I'd say a lot could do really well. Of course some would bomb and there would be a big learning curve that might take a year or two, but I'd say eventually a lot of faster marathon guys can make great ultramarathon runners. It would be an easier transition for them on a course like WS100 or Leadville even though (compared to UTMB or Hardrock). BM, yeah maybe not!
Part of it is having the running economy and musculature (variable to the terrain). A guy like Zach is probably actually more well suited (genetically) to a course like UTMB compared to Jim who is more suited for Western States (just by looking at their running form style and build and race performance history). But I think this year with Jim's very specific focus living and training basically on the course, dialing the gear and crew and nutrition/hydration and pacing was what earned him the win over Zach.
There are a lot of barriers to entry to get into a race like UTMB (getting stones/points just to enter, the travel there, all the gear, having a great crew/support team following you around). Then you've got to learn how to use trekking poles (or at least powerhike well) and be ready for 4000' climbs and downhills....also running at night in the mountains with a headlamp.
A lot of pretty good road runners don't know how financially lucrative it might be to switch to mountain-ultra-trail running in terms of lifestyle and sponsorship and travel opportunities. Not to mention the value of being able to gain more social media followers/attention by being a "big fish in a small pond" and running in some of the most beautiful places in the world.