I don’t think you know what monopoly means if you think Vanguard and BlackRock are a monopoly. (At least duopoly would be semantically possible, but factually still wrong)

If for example Russia and China together controlled a certain resource, then from the standpoint of the USA, Russia/China have a monopoly on that resource. Doesn't matter if Russia and China are in theory two different countries. They are in fact acting together with the same interest in this circumstance.

Follow ownership up the chain and you will discover the overall point is correct: everything is consolidating into fewer and fewer hands.

I hate this sort pedantry when this perspective dodges the ultimate lack of competing interests necessary for a market to produce goods and services efficiently. Just because our country has horrifically bad antitrust legislation doesn't mean we need to lower our discourse to that level. People have always used "monopoly" to mean "noncompetitive"; so just take it to mean the latter.