They solve the problem of centralized trust.
Whether it's Byzantine fault tolerance, or cryptoeconomics, there are some good solutions there. People's issues tend to be whether the solutions are applicable to the world, and/or useful.
I still hold out a hope (perhaps a fantasy) that all the talent and money funneling into all this, combined with the fundamentally interest and novel technology behind it, will come up with something truly innovative. It just seems like it must, right? But every new thing (most recently this NFT stuff) that comes out just further and further confirms my long-held tentative conclusion that there really isn't much there, there.
Pretty innovative and useful stuff...
Aave seems like something that is useful within the bubble of cryptocurrency traders, but not outside it. It strikes me as a meta thing, not a thing. It doesn't work if cryptocurrencies are never useful for anything outside that bubble.
Does Dai have a strategy for being actually useful as a currency to purchase things? Bitcoin has been trying to be useful as that for a decade with very little success.
Yearn seems to be in the same boat as Aave, it only exists in this bubble of cryptocurrency speculation.
None of this stuff or anything adjacent to it exists for anyone I interact with in my life outside of this website. What will blockchain technology be known for amongst people who are neither computer science nerds nor financial speculators? If it's just a new kind of speculative asset, like a new kind of derivative, then fine, that's innovative in a way, but it is extremely niche.
As for people who aren't building general-purpose distributed databases, a solution to the Byzantine generals problem is more of a solution to a problem that they don't have - as other posts in this thread demonstrate.
1) The original BTC paper was a huge breakthrough in decentralized systems.
2) Most "blockchain" projects today are merely elaborate Ponzis.