RB will not touch exported playlists on its own.  You have to tell it a specific playlist to export.

in RB, if you select a playlist and then export it to USB and that playlist is already there, it will first warn you that the playlist exists, and if you want to overwrite it.  If you say ok, it will then roll through and update that playlist and copy over any tracks that are missing.

RB will not, however, copy over the existing tracks.  This can be a problem if you have updated the track's metadata...it will not touch the existing tracks (say you updated the comment field, genre, key, etc... that information will be stale on the USB)

(Can't answer the itunes point, I don't use itunes at all)

I understand that, but im finding that rekordbox will copy over existing tracks on the device again, like overwriting not creating duplicates of the song, which then takes way longer to transfer the updated playlist of say 100 songs as apposed to the 5 or so new ones

it looks like it is, but it's not. :(

If I copy an already copied playlist, RB scans through all the tracks, and does so rather quickly if it is a fast device (SD is the fastest, FWIW.)  If I've added a track here and there, it will hang up and take much longer as it transfers over those tracks.  If it is a slow device, the whole process is realllllly slooooow...

If it is Apple Music Playlists, I think that it is unavailable because it is all protected by DRM. However, I have got a tool named TuneFab Apple Music Converter for helping me copy Apple Music Songs to USB for playing. 

@Aaron > Please don't necro-post; this topic is almost 5 years old.