Right, I agree. The theory is sound though. Theoretically, there could be a quantum computing breakthrough (however unlikely) which would break some traditional

Right, I agree. The theory is sound though. Theoretically, there could be a quantum computing breakthrough (however unlikely) which would break some traditional crypto which was previously deemed impossible. It is the same with blockchains. It is just that there isn't one that exists (yet) which has enough distributed hash power where it's infeasible for any actor/group to ever get 51%. Bitcoin is just the best example so far, some might argue it's still in its early stages, or that another blockchains will surpass it.