It's also currently only a subset of JS GC requirements at that. It's the bare minimum to share references between JS and WASM to byte arrays like Int32Array. It's like basic OS-level memory page sharing only for now.
Some of the real GC tests will be strings support (because immutability/interning) and higher-level composite objects, which is all still in various draft/proposal states.
Any language with advanced GC algorithms, or interior pointers, will run poorly with current WASM GC.
It works as long as their GC model overlaps with JS GC requirements.