securing a large financial network is not a waste.
or did you think the banks/visa/mastercard/paypal didn't use energy?
I'd say bitcoin is a lot more energy efficient.
The system of mining even encourages using energy efficient miners because f you use old models that use more electricity you will go broke.
It ain't energy efficient currently, but a lot more energy consuming currency, that needs a lot of miners to work behind it to be operated smoothly, and as per my knowledge, I haven't seen any miners currently available which consumes so less energy that they can get you ROI in less than 6 months...