A better argument here is that we must compare it to the current banking system. Sum up the cost of supporting banks, bankers, bank failures, runs on currency, etc. and bitcoin would clearly a good deal efficiency-wise if it was our main currency.
But banks provide credit which Bitcoin does not. Most of the problems with banks (bank failures etc) comes from the credit side, not the payments side.
At a glance, it might seem that simple. In more depth, people who try to hold money essentially don't have a place they can easily park and access it other than a bank. People get forced into a fractional reserve system. That fractional reserve system in turn needs a lot of extra work and systems behind it to function. Bitcoin is a way for people to keep and move money without being subject to either money printing or fractional reserve. So it is, in part, a replacement for that system.
Banks and Bitcoin serve radically different purposes. (Try getting a mortgage from Bitcoin!) A more appropriate comparison would be the percentage of bank energy that goes to payment processing, which is probably pretty low.
You should include the energy to print and mint notes and coins as well and the energy to make plastic cards.
What about all those air conditioned buildings with all those eating, breathing, commuting human beings everywhere? Bitcoin looks pretty competitive to me against that.
One major thing other than move money that bitcoin does is print it. If you also look into the complexities and inefficiencies where our money/debt come from I think you'll find they've very high indeed.