> Is it really all that difference from Apple defaulting to Google's search engine?

Not really, because the business model isn't there (at least not in this iteration.

1. The models are Apple models, co-developed with Google. They are not white-label Gemini.

2. There's not currently a Google failover or UX

3. Because of that, there's no user monetization to share.

Apple does have a ChatGPT integration, with failover UX, and with a suspected revenue share deal. However, one could see this deal in a precarious situation, since at the time it started it was expected Apple would not focus much at all on a model capable with world knowledge.

Depends on which way the money is flowing. Google pays Apple for default search engine. Is Google paying Apple for using Gemini? That feels like a much heavier investment if they are

Yes, Google can do that just like Intel, Samsung, Nvidia or Qualcomm yes Google can drag their feet, we know in the end it will all lead to tears and then they will separate.