There are actually improvements to the traditional infrastructure; Bitcoin mining setups are power intensive but are majorly run on renewable energy, report from last year by
Coinshares research says that around 74% of overall mining power is gotten from renewable sources.
The Bitcoin mining sector also functions as the 'buyer of last resort', so rather than it putting a strain on available power, it utilizes unused energy, reducing losses and could be a major economic driver in future.
And banks don't have any mining at all, so they don't have to spend any energy on that. And right now Bitcoin only covers how many, 700k transactions per day? This is nothing compared to Visa. Until LN is widely adopted, Bitcoin network is less efficient at per transaction basis.
Also, enviromental impact of both banks and Bitcoin is tiny compared to industries like transportation or agriculture. Even if they were 100% green, it still wouldn't make any difference.