Ya, that's distributed adversarial consensus. Decentralized currencies are an excellent instance of such conditions. They really are a useful and interesting application. That doesn't mean they deserve all this hype in the form of investment from the average person, but if they weren't so hyped, they'd have a serious use-case as a world reserve currency and they'd make a very nice international settlement layer. Because all of the countries in the world would know that the currency was politically neutral. I think that's a pretty sweet/useful property to have.
There are definitely a few other cases where adversarial consensus problems exist too. I think decentralized prediction markets are a pretty great application of smart contracts, for instance. But yes, a lot of these things are way way over-hyped and being pushed for things way beyond their useful scope.
"Permissioned blockchains" is like someone thought "what if we took the radios out of cellphones and connected them by cables" and proceeded to call that a brand new invention.