it's using dialup in some form while NFC is perhaps always online
That's nonsense. If the NFC is faster, then it's being cached. A less than €20 Contactless payment isn't verified in many countries, which is REALLY STUPID and allows the slurping of funds in crowded places using a cordless terminal.
You can tell shops using different kinds of connection from the speed. Most of the places I use with chip & pin are now almost instant.