Ocaml is a wicked fast compiler and a simple language. Having done both, I’d rather not do Scala again, but would happily do Ocaml if it had a better ecosystem.

Exactly! But Scala is out of fashion at hn these days

Not that I've tried ReScript but it advertises fast builds, which the (sample size of one) large scala codebase I've worked on was really slow to compile.

Yes, it pretty much depends on what and how you're trying to compile. Incremental complication helps a lot, as does keeping sbt shell open and not restarting sbt each time.

In other news: now, there's scala-cli for smaller projects — https://scala-cli.virtuslab.org/docs/guides/scala-js

this is true. ReScript/OCaml compiler is super speedy. Scala/sbt builds can usually be optimised quite a bit few people know how or bother to