If you only look at the energy cost of running the servers where the banks store their databases, sure. But what about the energy cost of powering air-conditioned and brightly lit office buildings all around the world, thousands of branches and ATMs, security systems such as secure vaults and armored trucks, and the millions of employees commuting every day (or in 2020, Zooming into meetings all day)? It adds up real quick.

The difference is that the Bitcoin network is completely transparent and auditable, and we can accurately estimate the total energy used to secure it; whereas the banking network is opaque and we can only guesstimate how much energy they really consume