Ah, that certainly is faster and more convenient, thank you for the tip!
Now, it would be convenient if I could import an entire folder of LUTs as a category without having to create a new category and so on. See, I may or may not have accidentally imported 45 LUTs into the default category just now, and I don't see a way to move them to another category en masse. Looks like they were imported into ~/Library/Group Containers/6LVTQB9699.com.seriflabs/v2/user/adjustments.propcol, but .propcol is apparently a Serif proprietary format – had it been, say, SQLite, I would've whipped up a tool for this myself...
Alternately, if I could just point the Affinity suite at my Resources/LUTs directory and have it read from over there instead of having everything in a single propcol file...
Well, I suppose it'd be good enough to lazily generate the thumbnails for only the LUTs that are visible in the list at any given moment