You're right. This whole thing is largely a commercial for the brands he's attracted. The charity angle is designed simply to bring the emotional side into play (very cynically, as he touts support for cancer research while also posting shots of himself smoking and drinking to troll his detractors). That said, there is at least the theoretical possibility that an ACTUAL ultra athlete could do legitimately what he's claiming to do, now that we know it's possible.
So in this sense he IS taking away opportunities from legitimate athletes-- people who might have both a story to sell and the ability to actually do the running. And, really, it would be an interesting spectacle with today's tech to watch someone try to run 100km+/day through some of the most remote parts of AUS, ravaged by the effort and the elements as they'd be-- much more compelling than watching some gym fit fraud prancing around, then trolling people in his feeds. (And, yeah, I suppose there's grudging respect for this guy's sheer chutzpah, but that's as far as it goes).