Off-chain solutions to the inherent inefficiencies of blockchain applications also sidestep the advantages that cryptocurrency proponents promise blockchains will bring.

Bitcoin is hardly cost prohibitive. When was the last time you sent a transaction? The last one I sent cleared at 2sats/byte and was <$1. Are you going to buy your coffee with it? No, probably not, but that hardly makes it a useless as currency replacement. Replace-by-fee doesn't make small transactions any less trustworthy either, since you should never trust any unconfirmed transaction (by definition, if its not on the blockchain its not yet a transaction). Furthermore, the lightning network blows away the competition in terms of cost per transaction, and while not perfectly trust-less (unlike the base layer) it has far less custodial risk than a bank or credit card account. If for example your counter-party goes rogue, at worst you just close the channel resulting in a rollback to the last settled balance state, minus an on-chain fee.