In "databases and journals" you rarely update just one byte, you do a transaction that updates data, several indexes and metadata. All of that needs to be atomic.

Power failure can happen in between any of "1 byte updates with crazy latencies." However small latency is, power failure is still faster. Usually, there is a write ahead or some other log that alleviates the problem, this log is usually written in streaming fashion.

What is good, though, is that "blast radius" [1] of failure is smaller than usual - failed one byte write rarely corrupts more that one byte or cache line. SQLite has to deal with 512 (and even more) bytes long possible corruptions on most disks, with Optane it is not necessarily so. So, less data to copy, scan, etc.

[1] https://sqlite.org/psow.html

It's not. You won't be writing one byte, ever (even if you had layers that actually supported less-than-block writes), because the overhead of instruction would be massive and you'd be murdering both latency and bandwidth for anything non-trivial