Banks don't do anything that can't be done by a machine.
To make an accurate comparison you would need to measure the amount held by banks, the amount transferred by banks, the amount transferred by places like WU, and the total energy consumption of all banks and MSBs like WU. You would then compare the amounts transacted with bitcoin (actual economical transactions) and the market cap of bitcoin with the energy consumption of ASICs and the energy consumption required to keep private keys safe
Those numbers have been roughly extrapolated. It will need to grow by a few orders of magnitude, but not much more. I think the OP was a little simplistic in comparing a person to an ASIC. It's not like anyone would ever replace a human job with a machine. While it's possible that Bitcoin's currency status will falter because fees get too high, Bitcoin metacoins will easily handle all electronic global transactions with machine precision and be fully automated. Bitcoin itself will not need to grow infinitely because local off blockchain servers and sidechains will mitigate tasking Bitcoin miners with trivial purchases.