>There's no net-value created by doing the 'mining part' - in fact, it's a value-destroying activity

You don't understand where cryptocurrencies derive their value from if you're saying this. Mining is what give cryptocurrencies their legitimacy, it proves that a digital file is scarce (important for information used to account for wealth/scarcity) and second it proves that the payment hasn't been double spent.

The traditional financial / political system, these processes are obfuscated or inefficient because you need lawyers, judgers, armed guards, vaults, auditors etc etc to preform the same task: to ensure that FedWire isn't inflating the supply, rolling back a payment.