It is, but you have hit the nail on the head in identifying the issue here as the smaller banks seem to have all opted to develop their own contact-based systems instead to create a network effect and lock people in with the ability to add richer transaction data, which has compromised the Paym pitch - it should obviously be just “every bank” (within reason). There’s no reason Monzo (for example) couldn’t offer Monzo.me, PayM payments and “traditional” sort code and account number.
All the big banks are Paym members, but many of the smaller and medium-sized ones aren’t.