If we have pokemon like Syclant and Revenankh in breeding groups, then they get egg moves. but in theory, don't they effect the breeding group as well. For example, lets say that we make a Flying Phys balanced pokemon, then give it Hypnosis and Brave Bird. well also placing it in the "Flying" breeding group. Not only have we created a OU Flying type, but we also have enabled Crobat to learn both Brave Bird and Hypnosis at the same time. In theory, this could disrupt the Metagame more than adding characters does.