Why on earth do you think that Doc Scratch had anything to do with the Lusus system?
Sure he’s responsible for introducing Feferi and The Condesce’s lusus Gl’bgolyb to Alternia but that’s it as far as we know.
It seems incredibly unlikely that he sat down one day and decided “You know what? All troll children should be raised by monsters. Particularly seeing how integral the idea of a Lusus Naturae seem to be to Troll culture and biology.