I think you would be better off looking at the spread among those top 100 players, rather than between those and some ill-defined "middle". There's no reason to

I think you would be better off looking at the spread among those top 100 players, rather than between those and some ill-defined "middle". There's no reason to expect the middle of the different Elo distributions to settle in the same place. Looking at the difference between the top-ranked player and the 100th, we get 240 points for blitz, 227 for rapid, 219 for standard. That suggests that among the elite, the best players are indeed more dominant at blitz than at longer time controls. However the effect size is small and you'd want to check for other effects causing this: eg pretty much all of the best players will be on the standard list, but some of them may not be on the blitz list as that is restricted to players who have played a rated blitz game over the board in the last two years.