>>308121 (OP)
>s2 intro
>Discord beat by more powerful magic
>s4 intro
>Discord too busy being a smug cunt to help anyone
>s4 finale
>Discord easily tricked into giving up his powers by Tirek
>s6 finale
>once again, more powerful magic than Discord exists to neutralize his powers
>and he only agreed to help because Fluttershy was in immediate danger anyway
In short, Discord will either defeat himself by being an asshole, or he'll straight out refuse to help because he's an asshole, or the writers can just write in some op bullshit that can beat him.