I'm aware that this was just for the purpose of showing the problem with out of context stats. But even so, I'm not so sure about that. Want to name some people who are sub 10 with Roux? 5BLD and biggreen are the only ones I know of. And you're close. But... three people?
If you are right about Roux having a higher percentage, it's because Roux is a more difficult method with a much shallower learning curve than CFOP, and anybody who is willing to take on that difficult a method is probably willing to take on being sub 10. CFOP is suitable for casual cubers. I've never heard of a "casual" Roux solver, unless you count the people who use CFOP as their main method and learned Roux just for fun. Point is, if Roux does have a higher percentage of sub 10 solvers, (which I sort of doubt, since I can only think of a few) it's not because the method has more potential. It's because the solvers who would take on Roux are the ones who would become sub 10 regardless of what method they were using. What happened to many of the Roux solvers who are not sub 10? They quit Roux and switched back to CFOP.