> The only thing you get to go off of is the Advertising Identifier and the user can change/reset that at any moment effectively not tying them to any specific targeting.

People say this a lot, but Apple disagree: https://support.apple.com/en-us/HT205223

Highlights: name, address, age, iTunes/app etc. purchases, offers in Wallet, news read.

There is an opt out of those ("Limit ad tracking") but by default Apple will target on those things.

Probably semi-irrelevant because of Apple stepping away from iAd but Apple clearly use the Apple ID to target advertising.