And if the global banking system was pulling 2% of global power consumption the shareholders would be fetching the pitchforks and torches. I have no numbers off the cuff but I don't see a world where banks would be dumping crypto levels of money into power and server use.
I don't think there are currently many/if any Bank's that require a data center to draw as much power as required by the cryptocurrency miners.
Furthermore, does this Bank serve the people of that country? Does that Bank provide jobs for people in said Country? Does the benefit of such improvements in security greatly benefit the immediate customers in said country?
Many more questions would need to be asked to answer that question.
The article points out that these miners use a disproportionate amount of electricity, whilst providing little to no jobs to the local economy.
Whilst we don't have the numbers here, it is a safe bet for the company to withhold energy capacity for the likes of electric cars and heat pumps etc.
(Arguably the use of AI for anti-fraud detection might start causing a bit of this problem)
Besides that, the banking system is already optimized due to the capitalism behind it.
Btw. The crypto bros tell you that this doesn't matter because you should use lightning anyway (what an irony)
Obviously the bank can do things in a much less computationally intensive way, but my point is would this happen if a bank decided to use some computationally heavy process in its data center to make its transactions more secure and it used the same amount of power?