> Other than immutability by default and pattern matching I don’t see the Rust connection.

They're both MLs with familiar syntaxes.

> Out of curiosity, what is OCaml’s baggage that you’re thinking of?

Dependencies on OCaml toolchain, standard libraries, and ecosystem (which seems like it should be a feature but in practice it just means you need to understand two languages, two toolchains, and the nuances of integrating them).