> compared to the existing banking system it's trying to replace

I don't think it's appropriate to compare it to the existing banking system (whose featureset goes far beyond payments and managing account balances).

It's appropriate to compare it to existing payment and account systems. And on that front, compared to e.g. Mastercard, there's no way Bitcoin is more efficient. TXs/watt, $/watt, however you want to measure it.