I'm well aware my body doesn't store enough ATP to run fast during 2 hours. That being said I can run slower and make it past 2hours on pure water. I can also run a 2 hours pace coherent with my 1hour pace without taking too much care about nutrition (some under dosage sport drink or a combination of 2gels and pure water or even gummy bears + water can do). So nutrition is a total non event there.
The need is not to replace everything you burn. The need is for what you have in store + what you ingest to be enough to carry you to the finish line. The longer you run, the less what you had in store helps. So even running a bit slower, there is a point where what you would need is actually more than what you can take without throwing up. Had to that the need to stay hydrated without throwing up electrlytes ballance, and you realize the longer the race, the more other talents than just distance running are needed to succeed.
I mentionned 100milers because they are extrem exemples of this eating and hydrating factor without the added factor of sleep deprivation (for elites on non extremely technical and hard ultras). In that sense, I view a fifty miler as some sort of middle ground between marathon and runnable 100milers.
I'm not saying JW's run was on the same level as EK's Monza, or Berlin18, or even London19. It was not. I'm saying though you're kidding yourself if you think fast marathon automatically implies fast 50 miler. Ask Andrew how 50K correlates with 50M.
Get it now?