Turns out the only gamelist that was created was in ~/RetroPie/roms/retropie/gamelist.xml , (there was only this single one on my whole disk, and I did search for hidden files, too).
But in the retropie_setup.sh -> tools -> scraper options, I had disabled (or forgotten to enable) that the .xmls be put in their respective rom directories.
So I deleted the single gamelist and image folder (that contained metadata for >10 systems), scraped again, since I really couldn't be bothered with manually sorting metadata for >4k Roms into different folders, and this time everything was saved to the right locations!
Thank you very much for providing me with the correct locations, the problem is solved now and the thread can be closed.