The point isn't that it's fine for smartphone car keys to randomly fail, it's that there's plenty of other reasons they can fail that you're already living on the edge if all you're carrying is your phone. Therefore the "it's dangerous to assume ..." claim doesn't hold.

> Apple Pay involves at least a third party (your bank) as a part of its function. This entity has to be reachable.

No it doesn't. It has to have a recent token, and if it does not it will contact your bank.