Not sure where you're coming from? Many (most?) UK retail banks use VISA for their card card network. I have VISA cards from HSBC, Barclays, MBNA, etc... In fact I didn't have anything else so I got a new AmEx when they said they were stopping accepting VISA.
Regarding the overall proportion, when the Amazon announcement was originally made Which? listed all the retail banks and other card issuers. MasterCard far outstrips Visa at a ratio of 3:1 (15 to 5): https://www.which.co.uk/news/2021/11/amazons-visa-credit-car...
https://www.headforpoints.com/2018/05/31/mbna-offering-uks-b...
No where did you read that? It's not true that all VISA cards in the UK are credit cards. It's just that only credit cards are relevant here.
> My DEBIT card is Visa.
Again... this thread is about credit cards, not debit cards. Nobody's talking about debit cards.
People who don't care enough would normally have been OK paying with their Visa Debit which they will usually also have as an HSBC or Barclays retail customer...
Section 75 in particular has a lot of attention in the UK because over the last 4 years a lot of businesses have gone bust, and people who paid by bank transfer or debit card were shafted, receiving pennies on the pound (if that).