That may be true by definition, if your definition is that superior groups eventually dominate, but that's of course just tautology.
However, depending on how you define "superior", for example "more intelligent and honest", or "more compassionate and fairer", could be what most people have in mind, then that may not be true at all. In human societies, throughout history, it's likely that who dominates is actually the most brutal and reckless, up to a point where people actually become accountable for their actions.
See, no, the second you put in "superior" then you left any idea of a free market. The idea of a free market doesn't claim to make any value judgement of what group is better, the free market is purely about selecting fair prices for commodities.
Your idea of superior groups and so on based on success on the free market is basically social darwinism.
Actually, free markets are only efficient if p=np.
(They are not strong form efficient, that was disproven long ago, and are only weak form efficient if p=np)
Unfortunately, this hasn't stopped people from believing in them anyway, because they really really want them to work, and people "feel" like they should
They still outperform other mechanisms we have of resource allocation. They're massively parallel systems with ample signaling of different agents' state.
And the worst corner cases of externalities can be mostly offset with proper regulation, even if we struggle to do it.
If you can consistently outperform your peers while both parties have complete information, it's a sign of having some advantage.
Free markets are never perfect locally, but on a galactic scale they are pretty close, so the superior groups and will dominate.