Ignore me! I found the solution...
There's a copy made to Camera Raw, so I had to delete those also for it to work.
I don't know if it's useful to anyone else... but what I also had to do was batch rename all the old presets to remove the ~ it adds to the filenames.
When you then copy these back into Develop Presets, it re-converts them to XMP and re-adds the ~ to the files (so I made a copy of the no ~ version before opening lightroom). It then keeps all the folder structure as it was before.
I don't know if I missed something, but what a pain if this is what you have to do if you decide to spring clean and reorganise your Preset folder!
Message me if you need more details of my solution.
having a similar issue im trying to clean out life presets and add new ones but it does not seem to remove the deleted I removed from develop preset folder from the Lightroom application and when adding new ones it doesn't seem to update also