“Maybe some DJs prefer a kind of oldschool approach without another layer of software like Engine DJ, just direct transfer of files and folders.”
How is this “old-school” ? This is simply how every computerized device stores files. Again, what the EngineDJ/Prime4 does is try and re-invent the wheel. It creates an extra Table Of Content for all your audio-files, while it’s already there! All it needs to be doing is scan your SSD or SD-card or USB-drive and create a database with all the info needed for the Prime4 to work with, like cue points etc. and then point towards the existing audio on disk/ssd/sdcard/usb. That’s NOT what denon decided to do, denon creates an entirely new folder-structure on your drive(s) based on metadata (which I described earlier is very flaky). I have no idea why they’ve done it like this, it’s a waste of time and doubles the disk-writes, and makes syncing of audio-files really difficult. Every file has to be passed through their database first, in order to recognize where it has put the file, re-read its properties, size, content, and then decide what to do with it while syncing. So weird.