I don't think there's much to assume here.

Governments around the world have rules about companies, salaries, taxes and so on.

There exist a large number of billionaires.

Therefore, assuming most of them follow the rules, the rules allow such a concentration of individual wealth.

I'm not against innovators getting relatively rich, that's often the incentive to innovate, or at least to push through the 'perspiration' part of that activity, but there should be balance.

Sorry, I was unclear. I was referring only to the last point (that that amount of individual wealth is a policy failure) when asking about axioms.

I completely agree that the current rules at least allow such wealth accumulation, which if applied across 8 billion people means that many will choose that path.

Well of course we can disagree whether or not billionaires are good or bad. I realize people at one extreme subscribe to the 'red in tooth and claw' natural law view of how society should be organized, and others to the opposite 'we're all in this together' view.

Personally I think the existence of billionaires is a systemic failure, is morally suspect to say the least, and that such extreme inequality is bad for society and slows progress, ultimately.