>...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.