My understanding is that Jane Street use their own, very custom, build rules, so it should be entirely possible to reconsider what the defaults are in upstream Dune. I’ve opened ocaml/dune#8645 to begin this discussion with some low hanging fruit. The complexity lies more in backwards compatibility considerations, but that can be handled by the versioned dune-project files allowing the change to be opt-in for projects as they upgrade.
I agree with this entirely. My own uses of OCaml tend towards the esoteric cross-compiling on embedded architectures 
And if we’re diving into strong opinions, I have a strong negative reaction to introducing a dependency on the JDK in order to build my OCaml project on some RISC-V board with tiny amounts of memory. I’m glad you have some use of Bazel, but it would be an entirely inappropriate default. But as I noted in another thread, your usecase isn’t mine, and I’m entirely supportive of seeing such alternatives in the OCaml documentation, if they pass a reasonable threshold of coverage and adoption.