I don't see what the issue is. The user could then select Apple (or Mistral) for strong privacy or another provider for customers that don't care.

I primarily want Apple to provide extension points so that I can select my own provider, just as I can choose where to host my mail or install another app as my instant messenger.

Sure, I could install another provider's app, but it wouldn't have the same integrations, similar to how an instant messaging app would be less useful if notifications were limited to iMessage.

I'd love to select Mistral over Google Gemini.

Sure.