> If you run a libre device without the Google Play store (non-Google android build) then the software cannot function

I think you mean either of two things:

1. running the APK they build on a device without Google Service does not work

2. running the APK they build on a device means it's no longer running only libre software

1. is not true, so I assume you mean 2. I guess that's true, but in practice I think that the compiled dependency doesn't do anything if you don't have the services on your phone (don't quote me on that). It's not free software, but it's still better than the competition.