What efficiency do you mean? 7 transactions per second is not very efficient — VISA can do nearly four orders of magnitude more. Even if you believe in big blocks and other stuff — how that can increase efficiency ? 10 times? Still three orders of magnitude less than just one fiat payments processor. Cryptos cannot takeover fiat money and banks and other intermediaries— because distributed consensus will never be efficient enough for that. Maybe they could play a role similar to gold (with which we don’t do as many transactions — but we do some very valuable transactions) — or maybe as some kind of settlement layer for a Lightning network (which would constitute an payment intermediary then). But that is ignoring all kinds of political and economic variables.
Currently bitcoin and other Proof of Work cryptos are bleeding money on mining: https://medium.com/@zby/proof-of-work-8d8265def194 We don’t even know if a decentralized Proof of Stake is possible.