as one of the guys who helped make the decision, I agree it is kind of arbitrary. but, Pomeg presented an opportunity for several Pokemon to become viable when they hadn't previously, whereas rage+transform had the significant downside of completely destroying any semblance of balance not only in Our Faire Little Cup, but in all the tiers. wonderful as I am, I don't have the right to make a call like that, so that was never on the table. Nobody but LC gave a fuck about Pomeg, so it stuck around.
PLUS it benefited my favorite mon, Porygon ^^