That's a valid point. Being native to the host language (Rust) is generally a big advantage.
I just don't really understand why Rhai uses an AST walking interpreter, that's basically the least efficient way of implement a scripting language. Once you have an AST, a byte code compiler/interpreter is not really hard to implement, so I'm wondering why they knowingly leave so much performance on the table...
I gave Lua a shot, but getting the toolchain set up in wasm was a hassle:
https://bytedream.github.io/litbwraw/introduction.html
So at least I can say Rhai has some advantages on syntax and compatibility with wasm