As if any Kamen Rider villain is more powerful than Fog Mother. As for Sentai, isn't Black Cross Fuhrer invulnerable to the point where hydrogen bombs can't harm him unless you hit him with cosmic rays from his home constellation?
The Great Leader is just a dude with a monster stuck on his head. How does that compare to LIMITLESS COSMIC POWER or whatever that guy Shark said can do.
Hardly any KR villain could destroy/take over the world without some kind of doomsday weapon.
For Kamen Rider, it would be the Great Leader. Since he keeps coming back, to where the Riders hope he stays dead this time. But for Sentai, that's very difficult. Since the only that was the closest was Zangyack, due to them costing 34 Sentai their powers. Only to lose out to the Gokaigers, because they underestimated them one too many times.