It is quite preposterous to claim that "OpenAI" is a "startup". Neither is it "Open" while we are at it.

I don't think the word "startup" is especially apt either, but that imprecision doesn't change the validity of the argument.

Well let’s see the Amodei siblings left and we got Anthropic. Ilya left and we got SSI. Mira left and we got Thinking Machines. So it seems we can break it up and actually get even more innovation!

You're not "breaking it up" in this instance; you're just killing it. You can mechanically generate new competition by killing any company --- new entrants will rush in to fill the void.