I'm doing pretty good, and I grew up dirt poor. It's possible for the rest of us to invest in the Stock Market as well, it isn't just restricted to the rich. That said, I won't deny I've had certain advantages. Like not having a gf most of my life. Not having kids will do wonders for your financial situation. And really, not having kids is the best option for the environment.
That others may invest some (by comparison infinitesimal) amount somewhere, or get analogous infinitesimal gains, doesn't mean anything about who the system is made for. I mean... 500 people adding more than a trillion to their already colossal income in 2017? Makes no difference if any random middle-ish class person gets a few more thousand $/year.