That's only true if the allocation decisions are being made by a third party like a VC because the third party usually has fiduciary duties (otherwise you have problems with conflicts of interest). But if the billionaire is investing his/her own money I see no reason their risk posture should be any different whether they're investing in their own venture or someone else's.
That is what the original commenter meant. If there are Elons out there with no money, they could band together to go to a VC, but then the risk taking process is skewed, because the brains and brawn are distributed.
