That's where my head is at. They're building and improving it. Legacy banking isn't exactly green itself, as card transactions have a pretty hefty carbon footprint. Further, banks are eyeballing their own "CBDCs", which is basically cryptocurrency but without the intended benefits of decentralization.

Zero knowledge roll-ups have a lot of green promise with gas fees... but DeFi isn't better than legacy banking yet. Still, I think it will be sooner or later if only because some of those folks are actually trying to improve it (where banks are only really doing their best work at trying to get more exploitative).