I do write some code using FFI, but I have a cffi layer in there for PyPy. I do not interact with the CPython API.

Currently I don't have an interest in taking time to try and make PyPy less slow for my use case, for many reasons that I'm not going to get into here. (But I will note I'm primarily writing code that focuses on being easy to distribute. Most users aren't going to have PyPy installed anyway.)

Anyway, the main thrust of my post is just that Python isn't a monoculture in which PyPy is always a better solution.