I don’t think exporting will clean up the mess. I’m not an OSX guy so others will have to take it from here.
My thoughts, for what they are worth, Roon doesn’t really care much for folders and tags. My library was pristine in terms of all that. Roon does things their way. I had to do some tweaking to get it looking as slick as possible.
Might want to download mp3tag, create folders for each artist, put each album under the artist with their files - but, again, not really necessary for Roon.
BTW, I moved all my music off a Qnap NAS and put it on a SSD internal to my Core, but an external drive on your core will do the same. Much faster and any changes to your library happen in real time and, therefore, no rescanning necessary.