[gnaritas]

> The popular narrative that, unchecked by government, a business will eventually rise to absorb everything is not borne out by practice.

There is no such popular narrative-that's merely a strawman you've created-the popular narrative is that monopolies can and do form (not always, but can) in the absence of government rules to prevent them and that such monopolies are bad for capitalism. That is a fact borne out by history.

> Rockefeller is mostly guilty simply of being very rich

No, he's guilty of abusing the power of his near monopoly to sabotage competition just as the OP said. He's not reviled for his wealth, but for the unethical ways in which it was maintained.