I’m afraid It will never work as you expect!
My LE preset detach highest note of every “properly played” chord and move the rest to the lower staff, and it does work. If it doesn’t for you, either you didn’t build the preset correctly, or you didn’t configure your staff correctly, or you didn’t played well enough the chords for their detection.
It would have been helpful if you had precisely explained what you did and what were the results?
Besides, I don’t see how it would be possible to make Cubase automatically separate the melody from the chords in a played sequence. It is also tied to the way the program detects chords.
Probably an A.I. would do the job 
Your best bet is still the Split mode in Score Editor.