What you've been told seems to be erroneous. See Category:Reggae rock songs for example, which features reggae rock songs by artists whose main genre is not reggae rock (eg The Clash). Also "hlists" are more readable than "flatlists" and exactly work the same way. So there's no reason to change one template for another one... Finally adding "hard rock" within buddling references is useless if the references are next to the sourced material.