Oxytocin certainly bonds members of animal and human groups, but it’s not as easy to separate the hormone’s biological, evolutionary function from its exaptations or creative co-optations in an emergent social context. There’s the bond between parents and offspring, which would be necessary for the species’ survival when the parents are needed to train their young, as is usually the case with social species. But the broader uses could have sociological rather than strictly genetic and evolutionary (natural selection) explanations.
The article below shows that oxytocin in chimps also functions as a warmonger hormone, since it bonds the chimps with feelings of loyalty to prep them for war. Likewise, mothers have to protect their babies from threats, putting their lives in danger, and the oxytocin bond is at the root of that sacrifice. So the love bond goes hand in hand with aggression towards outsiders.
I hardly think the wealthy dominate because they excel at cooperation. The urge to compromise and cooperate is closer to what Nietzsche called slave morality. The wealthy are the free-riders (parasites) who exploit most people’s meekness. Behind every great fortune there’s a crime.