Just a backup though, the main metadata is in the MC library. The sidecar files are mostly a backup in case you need to re-import the files.
Or share them with other systems (copies of MC mostly, though I have tools that use the XML for other ends).
One problem with using a subdirectory is file path length limits. It may surprise you, but users here hit these limits with some regularity. Especially if they use system folders to store files, so they start already fairly "buried" in the directory structure on disk.
The benefit of always using the exact path of the source file is that you don't have to "check" that the path of the sidecar file will also be valid. If the source can be there with that filename (and it already is there before the sidecars are created) then the sidecars will be valid filename as well. Since moving the files with RMCF is done separately from creating the sidecars, it could be fairly complex to manage the path length limits otherwise.
Other possible solutions to that issue can risk collisions if the user doesn't have folder structures organization like you might expect.
Not saying is isn't solvable, but it isn't super simple. I think the decision was that this is "good enough", and if you don't like it, turn them off.
