TLS != crypto. TLS is actually very well-suited for a higher-level language like Rust or OCaml, especially due to how state machine patterns can be expressed safely in those languages. Crypto, on the other hand, often relies on low-level intrinsics to get good performance and cache timing attack resistance.

TLS depends on crypto and the mirage team implemented it using OCaml. It supports low-level intrinsics for timing attack resistance. See: https://github.com/mirleft/ocaml-nocrypto