Their competitive advantage is not so much running the browser but rather making the browser undetectable.

They boast a large residential proxy network too, which tells you all you need to know.

Or processes. Chrome has builtin process isolation for every browser tab. It starts up darn near instantly, and scores as 'pretty good' as far as sandboxing is concerned.

docker is not a security boundary but a resource boundary.

Docker does not isolate, consumes more resources and is slower