>...blockchain is going to be overkill for dealing with some types of fault tolerance
But it this case likely it isn't. The current systen already works with a chain of blocks its just lacks the distributed checking and all that stuff. But "blckchains" aren't some secret sauce in this case it just an way to implement a distributed write-only database with filed proven tech. It can be as lightweight as it any other solution. The consensus part is completely irrelevant anyway because all nodes are operated by one entity. But due to the use case (money/value) of modern DLT ("blockchains") they are incredible reliable by design. The oldest DLTs that uses FBA (instead of PoW/PoS) are running since 9+ years without any error or downtime. Recreating a similar reliable system would be month and month of work followed by month of testing.
I thought you were making a more general statement about all critical systems, that's all. And since many critical systems have a safety factor in play, I wanted to distinguish them as not always being a good target for a Blockchain solution to the problems of consensus.
Blockchain is a very interesting solution to the problem of obtaining consensus in the face of imperfect inputs, there are other options so, like anything else, you choose the right tool for the job. My own view is that-- given other established protocols, blockchain is going to be overkill for dealing with some types of fault tolerance. It is a very good fit for applications where you want to minimize relying on the trust of humans. (And other areas too, but right now I'm just speaking of the narrow context of consensus amid inconsistent inputs)