I think they are a pretty fundamental innovation in that space.
What are good alternatives? Gold, cash, or ETFs have substantial drawbacks - especially in situations where property rights are insecure and inflation runs wild (or just eats up savings at a somewhat moderate pace, as is the case in many developing countries).
Of course Bitcoin is also a human system, eventually, but what you are trusting is an emergent, non-hierarchical order which should be more resilient than hierarchical systems. The technology facilitates the emergence of such a system.
I actually think the flawlessness of the technology is not a necessary condition of Bitcoin's success. If bugs are found then consensus in the social system can emerge which can minimise damages
All of that being said I think the use case for blockchain is probably quite narrow.