I agree with the point you are making here. I just think that Proof-of-Work is usually a better choice for a cryptocurrency than Proof-of-Stake.

Conventional currencies (notably the US Dollar) are also backed by signifigant military (and thus electrical) power. I would posit that Fiat currencies are nessisary in some sense, but not that they are more efficient to maintain than cryptocurrencies. Cryptocurrencies tend to piggyback on the infrastructure and economy that are built on fiat (e.g. The internet).

We wouldn't have to overthrow mid-east dictators every time they threaten to price oil in Euros -- but obviously this wouldn't help much because we'd still need to maintain superpower status or risk losing the world order.