I know the common response in this thread is, "duh, yes," but I'm not sure it's that clear. Let's say Rupp has Walmsley by about 7% over the marathon distance (9-10 minutes). How long is that edge maintained? To 30 miles? Sure. 50? I'm less certain? 75? Far less certain.
How about with more than ten times the climbing? (in just its first 4 miles, Western States has almost twice Atlanta's climbing) And then 23,000 feet of descending?
I don't think it's at all clear that Rupp's running style and raw speed give him the edge at something like Western States, and this doesn't even get into issues like hydration, fueling, weather, terrain, and mentality.
It struck me watching the Trials on Saturday that Walmsley may not be built for pure, high-speed road racing, and I'm curious to see how that works out at Comrades (he's clearly no slouch, though, given his 50-mile record). When he was in the same TV shot with Lagat, it really emphasized that Walmsley's running style appeared far more vertical, and perhaps not as efficient as the road runners. But that style isn't too bad for flying over rocks, roots, and the other crap along the trail.
Interesting thought experiment, though.