https://support.apple.com/en-us/HT202303

Is there any evidence that Apple is lying, and is actually decrypting them and using them for advertising purposes, rather than for the "coherence" feature?

I don't actually want browsing sessions to be unified across devices, so I do wish that it was turned off by default. (Though being able to close tabs remotely is a sort of interesting capability.) However, it doesn't seem to be actual spyware used for advertising or tracking purposes.

And it’s not going to google first. If you type an address the “link” at the top is to Apple Maps. They seem to do a similar thing with place names. I’m not sure but one can be fairly certain they’re using the phones location to help….

Is it? How exactly are encrypted payloads to a secure, opaque and generic endpoint easy to distinguish?

For spotting it going to Apple you'd have to do more fancy correlation over time and such, but you can find people out there who are researching this stuff... so that's who I'm waiting for to hear more from.