This whole malleability fiasco has shown once again that zero confirmation transactions can not be trusted.
since its not practical waiting for 10 minutes for a payment to clear when buying coffee it seems to me that bitcoin will never go mainstream in physical shops.
any solution involving a third party to clear payments defeats the whole purpose of bitcoin.
any third party will effectively turn into a bank along with all the classical fractional reserve practices we have today.
bitcoin is already available in atleast 30k businesses so part of your statement is false.
but when it comes to fiat.. bank transfers take 3-5 days, bank notes have a daily withdrawal limit. and as such debit/credit cards were used to solve these issues.
at the moment a few companies are working on a payment method that you deposit into and use for your pocket money needs. and as such because its deposited(preconfirmed) into a company that other businesses will trust. then INSTANT transactions can occur. either onchain or offchain.
visa/mastercard is a layer ontop of bank fiat.
these pocketmoney services are a layer ontop of bitcoin.
and as for the title of your thread. bitcoin is not even trying to replace fiat. its succeeding in working alongside fiat.