It does sound like it's not worth it to go back to stock. Maybe I will do that at a later point in time when I have a serial cable from work. I don't have one myself.
But now I'm curious because my serial number indicates that I have an older version. Could be that I send the first one back, because I didn't want to open it and still had warranty. Playing the dumb customer can pay off. Maybe I go an old one then.
Does it make a difference if I flash a region version or non-region version if there is no region lock? I'm not sure anymore, but I think there was no lock, because I don't remember including anything like that in the image.
@Borromini Thanks for reminding me for the procedure with the settings, I might have forgotten that!
Edit: I found that site: http://www.friedzombie.com/tplink-stripped-firmware/ for stripped firmware. Seems like I can just flash that from OpenWRT and I should be on the stock firmware and on the newest version. And from there I should be able to go to LEDE. The only question is if that means the bootloader was updated...