I mean I pay for shit on my iPhone with PayPal, "Shop Pay", "Amazon Pay", or direct CC entry -- not digital goods obviously but still it's a frame of reference. None are half as good as Apple Pay's "hit button, double click, FaceID, done" flow. Like I will actually switch to using my phone to make purchases because I don't want to enter my CC info on some random site.

Your experience with other payment processors on an iPhone are indeed not as good simply because they aren't allowed to be as good. Every single one of your experiences with these alternative payment processors was forced through a Safari browser.

Nothing is stopping the 'Shop' app or Amazon app from being used for any and all third-party (or fourth party, in this case) payments, as long as they're not selling purely digital goods.

If Apple wasn’t user-hostile this would all be an API that any payment provider could use.

I still prefer "hit button, tap TouchID, done".

I also wish Apple would make it easier to switch to a different credit card for a one-off purchase. And stop forcing everyone in a Family Sharing group to use the same credit card for all purchases

Argh, every day I consider going back to my iPhone 8 Plus purely because FaceID is so terrible. The point about switching cards easily is also absolutely right, plenty of places don’t accept American Express which is my default card.