Fair, but how many small businesses who are unable or unwilling to set up a payment terminal will be able to maintain the infrastructure needed to participate in a distributed consensus network?

There will still be an intermediary to whom the small business will pay fees for a turnkey solution. And absolutely those fees would be lower in a world where anyone can participate and compete on them. But that's definitely not the world we live in just yet, and even if/when it arrives, I don't think anyone at the retail level (either the consumer or the storefront) will have an appreciably different experience from what they have today.

EDIT: Just adding also, clearing times is the other huge barrier. Obviously no retail environment can tolerate a transaction delay of more than a few seconds, so the other function of the intermediary would be to manage that reality, by some combination of pre-clearing transactions for customers who look safe (classical CC fraud detection where de-anonymizing would be a key component), or maybe a pre-paying scheme (which ends up sounding a lot like a bank debit card).