I'm 25 wrote:
His body, heart and lungs can handle it. He is mentally stronger than anyone currently doing ultras. If he was working 50-100% harder (in some objective sense--calories or METs) than some MUT veteran on some technical ascent in a 100k, he'd STILL win. His long distance running proficiency absolutely extends to ultras.
For his marathon ability to be nullified, the race would have to be so long or so technical that it would be more about sleep deprivation or orienteering for others to gain advantages over him.
This may be true BUT for some reason it reminds me a bit of all these posters suggesting Jeremy Wariner should run the 800m or Warholm should run the 800m or Bolt should run god knows what…