First, what bitcoin tries to replace in the banking industry is not so clear cut. It could be payments, but also investment (value store), funding, and even credit. This very much depends on how successful and flexible the technology turns out to be. It is very early to say.
Second, the resources used by the banking industry to provide the services they do are not limited to the direct associated costs: we also have technology development, personnel costs (including energy used by the banking personnel to reach their workplace, the costs of turning on the lights in all the bank offices, and the fuel consumed by the bank managers to attend the party on the other side of the country without which the industry can not function, since, you know, you need some fun in order to sign the required contracts), the fuel consumed by the customers to reach the branch where, for the third time, they are going to evaluate their mortgage application, ... A long list.
In summary, yes, you are probably right that bitcoin is currently inefficient, and that currently it is not providing much value. But the sector is ripe for disruption, it is easy to disrupt, and any change in the current status quo will be an improvement, since the banking industry is so hugely inefficient for society as a whole.
At the core, the banking industry is just information processing, and that is the cake that technology is eating at the moment.