While of course finding a way to speed this up would be preferable (if it can be done safely and efficiently at the same time at all, with no way of just getting a consistent atomic snapshot of a directory from the OS) I’d say to not let perfect be the enemy of good.
Just general awareness would go a long way here. Ideally making it into the documentation instead of the laughable “will provide a small improvement in performance” and maybe even some runtime warning if the scan takes more than some time (5 minutes? 1h? 12h?).
The last use case I mentioned with WhatsApp directory is present in some places (one example below) but I’ve found NOWHERE the simple fix to just flip caseSensitiveFS. People go on all the wrong tangents while investigating this, including recommending other tools. While there’s nothing wrong with it, it would work quickly, reliably and efficiently if only this extra (completely unnecessary in this case, as in most) safety check is disabled. This would also benefit people thinking it works fine for them if the scanning takes an hour (but don’t know it could finish in 5s), and who don’t realize “works for me it doesn’t work for you” hits a user for which it would finish in 1 minute but it takes a week (and it actually never finishes if it gets restarted from time to time on the phones).