The solution should be a combination of folders and tags. E.g. imagine a folder that just contains all your photos without any substructures. It would be easy to just select e.g. all "2018 photos", "birthday photos" or "photos of your parents" in there without needing specific subfolders for those things (especially since those subfolders would conflict with eachother).

But I agree that I wouldn't want those pictures to be mixed with e.g. other random screenshots or drawings that I made, even if they could be separated by tags somehow. So folders as a hard separation would still make sense.