Outrage on mix goon isn't all glory. Yes it solves a lot of mix goons problems, namely blissey and sp. def physical walls such as hippowdon as mentioned above. But it doesn't ohko them, which is a problem when they are commonly paired with either skarmory or forretress. Suddenly mix flygons greatest strengths against stall (switching attacks and saying "fuck you" to entry hazards) become his biggest weakness. That said, due to his entry hazard resistance and immunity to sandstorm, roost is often a wasted slot anyway.