Did these Ocaml maintainers undergo some special course for dealing with difficult people? They show enormous amounts of maturity and patience. I'd just give the offender Torvalds' treatment and block them from the repo, case closed.
I wonder if it's the best outcome? The contributor doesn't seem to have a bad intention, could his energy be redirected more constructively? E.g. encouraging him to split up the PR, make a design proposal etc.
There's value in the PR in that it does not require you to install the separate OxCaml fork from Jane St which doesn't work with all the OCaml packages. Or wasn't when I tried it back in August.