I think a better example would be high speed trading and similar.

Of course any big corporation or administration is going to have a lot of underused ressources and redundancy but it doesn't mean they burn power "for the sake of it" as bitcoin does.

Also, bitcoin is not a bank, it's supposed to be a currency. If big banks were to switch to bitcoin I don't think they would spend less energy doing all you said. So no matter what you think of bitcoin it's fair to say it's not very "green" so far.

Greener than digging up precious metals to melt into blocks to be buried again in safes.

A better example than Bank of America would be a payment system like VISA.

That only accounts for a small fraction of the inefficient bloat of Big Banks