I've played every main FF game except for 3, 11 and 13. The problem with FF main villains is they either use some gimmick to achieve their mass destruction and/or reality/time alterations, or despite having that kind of large scale power they lack power in a direct fight.
Example: Necron, if he is to be believed, was going to wipe out all life in the universe. Despite being that powerful, Dagger summoning Bahamut or Steiner hitting him with his sword was still capable of shitting on his face, despite Bahamut not even being able to achieve city wide destruction in one shot. Powerful on a cosmic scale, weak both offensively and defensively in a direct fight.
SS4 end of GT Goku can do all that cosmic reality destroying bullshit that Necron can, but he's ridiculously strong in a direct fight, unlike Necron.