Use the organizer tools to create your own ways of grouping photos.
You can assign a given keyword to all the files in each subfolder.
Or you can create an album in which you enter all the files of the subfolders.
If you have a way to select all the files in the subfolders of that empty master folder, it's like having all the files at once in a single folder. You can sort them by date, file name, batch import. If you have an album you can sort them in 'custom' order without moving them in the drive.
Tip:
If you have more than a few subfolders, you can select all the files in the subfolder tree.
Start with checking that you have no disconnected files.
Outside of the organizer, from the Explorer or Finder, rename the empty master folder.
In the organizer do a search (menu Find) for disconnected files.
Select all (Ctrl A) and assign the same keyword.
Rename the master folder back to its original name and restart the organizer. Then you can select all your files at once and possibly store them in the same album and sort them freely independently from their subfolder location.