You're sort of implying that "free riders" were less of a problem earlier in our history because aggressive coalitions of lower ranked members were able to forc

You're sort of implying that "free riders" were less of a problem earlier in our history because aggressive coalitions of lower ranked members were able to force the hierarchy more in favour of egalitarianism. But that is hardly supported by the facts. Kings are an obvious counter-example. The caste system in India is another good example of a structure that were very robust (for many many many years) against any kind of aggressive revolution from below.