Hi Jee
As long as you have the option to read/create sidecar files switched ON (via Preferences) then all your edit/correction details are stored in the sidecar/.dop file associated with each RAW file … and they’ll be re-ingested into a newly created database the next time that PL encounters that folder.
All the same, you should make the decision to delete the database with care and understanding - for example, if you search by keywords then that’s done via the database - and you will have needed to refresh the database from all folders containing sidecar files before that process will be complete again
Note: There’s an option for that: 
The reason I noted, in my test, that I had deleted the database is that PL will not apply one’s automatic preset if the RAW-image is already listed in the database - So, that step was needed to ensure that each RAW was deemed to be a “new” RAW … in order to have WCS=Classic override the existing W-G setting
I could equally have selected all RAWs in the Image Browser and changed the WCS setting in-bulk.
You’ve not missed anything that I can see - - - All I can offer is this;
-
I repeated my test (on 1192 “new” RAWs) with my Preset having WCS=Classis
– All images loaded in a couple of minutes, and I could scroll to the bottom and see them all. -
Same test, this time with my Preset having WCS=Wide-Gamut
– It took a little longer to load the images, after which I could scroll to the bottom and see them all !!
So, it looks like that was not the cause after all - and it seems the problem is not evident all the time (at least, not on my system) … Mmmmmm !!
John