Interesting, I did the same with an old RTS and it also worked very well.
But instead of cloning their assets and rewriting their code, a dynamic x86 to WASM JIT recompiler with some web platform support code proved fast enough to run the original binaries. It is even playable on an old Android smartphone in Firefox.
The final web player is ~600KB and only needs the game installer as input, so people still have to buy/possess the game. I think this is a lot fairer for the original devs...
Which RTS is it? I'm a fan of the genre.