Mining is literally "hacking the security of the coin, measured partially." The whole point is to incentivize mining instead of hacking because they'd both benefit equally from the same discovered flaws in the crypto. That ensures the crypto (which can be swapped out if a weakness is discovered) is essentially impenetrable.

Mining also serves as THE first-known solution to the byzantine generals problem, which is a problem in every decentralized system that needs to agree on the canonical truth. What less-energy-consuming system to solve this problem would you suggest instead?

Yeah, this costs energy, but it's sort of like expending energy to shoot ammunition at a wall constantly in order to know right away as soon as any weakness is discovered.

What is the price of being unable to be hacked (see: Equifax)? Right now, that price is "mining energy expenditure."