The problem is there are multiple competing priorities at play here. I'm sure the dev team is aware of the poor WASM support. Still, as stated in the OP, they seriously value the ability to efficiently rewrite their current code in a more performant language without drastically altering it. Obviously, to someone depending on WASM, the latter brings no value to them, so they can more easily criticize the dev team because they are simply ignoring that priority.
If this is also priority, wouldn't Rust be the right choice? I’m not sure Go and C#’s WASM story is that great.