[throwaway894345]

It's very similar to the Python/C distinction. Python will often drop into C for the use-cases you're describing. However, unlike WASM, Python/C is the wild west:

- The whole CPython interpreter is the "C-extension interface" which means that the CPython interpreter can hardly change or be optimized or else it will break something in the ecosystem (and for the same compatibility reason it's virtually impossible for alternative optimized interpreters to make headway), and because the interpreter is so poorly optimized the ecosystem depends on C extensions for performance. WASM presumably won't have this distinction.

- Without the abysmal build ecosystem that C and C++ projects tend to bring with them, building and deploying WASM applications will likely be pleasant and easy after a few years. Of course, if your WASM is generated from C/C++ then that's a real bummer, but fortunately this should be a much smaller fraction of the ecosystem than it is with C/Python.