you'd be surprised at how much your system writes to disk.
If you haven't - I strongly suggest you run a week or four of write counts - tally it up and see what apps are doing it. You'd be surprised that some applications write ALOT to caches - say to speed up rescanning a file for a virus when new definitions come in by keeping a hash for a period of time. Some apps for instance keep a file per file Think about that. Doesn't really matter if they kept a sha for each file, in one big file because they would probably read-write the data anyway making small changes like timestamp so they know when to next check the file.(I'm talking to you SEP/Norton).
Some backup software keeps a lock of pointers too. If you think about it, distributing the work across the day rather than at one time makes it feel less invasive, especially with an old 5400rpm drive and not enough ram swapping cpu. However the caching may be trading drive write (which for hard drives, doesn't matter much) for speed.
I think Windows needs to come up with a super-tiering filesystem so we can do the SLC(20gb) -> MLC(256gb) -> TLC (2TB) shuffle dampening writes to the lowest tier.
It's very well possible someone can do this in controller, but the application/os layer probably can do a better job since it knows intent. Throw all that caching at the SLC, arrange the writes so that compression and dedupe is given intent to the filesystem and let it do its job best - as a filesystem