I'd wager that for 99.9% of "Apple Intelligence" tasks, Google's models perform just as well as other frontier labs. Google also has done more work on getting LLMs running on edge devices compared to anthropic and openAI.
The source also says > The new architecture centers on Apple Foundation Models co-developed with Google, which Apple says are adapted to run both on-device and on servers through its existing Private Cloud Compute infrastructure
Which could mean Google and Apple have trained some custom models, probably the on-device ones, specifically tailored towards Apple's hardware.
That's not the point of OP. The point of OP is that Google is a direct competitor of Apple for phones / OS, so them giving the "key of the house" to Google is risky