[mrb]

«If you're a small business, this matters a LOT.»

With a CC it takes 1-3 business day for the merchant to receive spendable funds. With a crypto tx it takes minutes (the time for 1 confirmation). This is a huge advantage for cryptocurrencies.

«What service, exactly, is more expensive than a 7% fee?»

It's the worldwide average of all remittance companies. See http://remittanceprices.worldbank.org/en which claim 7.13%.

«Major cryptocurrencies currently don't do it, so we shouldn't talk about them as if they do.»

You spoke as if the problem was unfixable. I am clarifying it can be fixed. The reason most cryptocurrencies do not implement UTXO commitment sets is simply that having to store all txs is not (yet) an intolerable pain point.