"It's only wasteful if there is a better alternative, which there isn't so it's not."

The alternative is to get by without it. There are fiat currencies, proof of stake and much more.

Capitalism of any kind always seeks to exploit externalities. The cost of producing electricity is currently not reflective of the true future cost of the pollution. That is the externality. Every metric in a capitalistic system is designed to reward the exploitation of externalities.