F# isn’t purely functional, though, and strikes a nice balance. I just don’t really like the .NET ecosystem, being 100% Linux these days, as it always seems slightly off to me somehow.

Same. I strikes me a great shame that there aren't great F#-like languages that targeted the JVM.

Really? What's wrong with .NET? It's one of the nicest cross-platform platforms out there. What Microsoft has done with it is amazing.