> and so de facto controls the ecosystem

They really don't, less than 5% of opam packages depend on Base and that's their bottom controversial dependency I'd say. Barely anyone's complaining about their work on the OCaml platform or less opinionated libraries. I admit the feeling that they do lingers, but having used OCaml in anger for a few years I think it's a non-issue.

What they do seem to control is the learning pipeline, as a newcomer you find yourself somewhat funneled to Base, Core, etc. I tried them for a while, but eventually understood I don't really need them.