Look at Gudis the second, or Gatanozoa. If you're going to tell me, with a straight face, that Godzilla was more of a threat than those two, I can't help it if I bust into laughter. Vacuumon ate stars, Zetton fired trillion-degree fireballs, Bulton could alter reality. Hell, Geronimon was the actual "king of monsters", and could ressurect fallen kaiju to serve him.
Originally I was referring to the original Ultraman for this fight, but since Megaloman brought it up, yes, Ultraseven had no preset time limit.
Ultraman Leo has the distinction of punching a hole through a powerhouse of a monster (seriously, a solid cylinder of flesh popped out), decapitating it with a sword that he pulled out of mid air, and THEN blowing it up. Ultraman Dyna had a ridiculous number of abilities at his disposal, including a beam that could very well have destroyed cities. I love Godzilla and Gamera, but when it comes to most Ultras, those two simply "run of the mill" monsters, differing very little from the norm.
Godzilla and Gamera may be among the strongest kaiju in their respective universes, but then again, monsters aren't quite as prolific as they are in Ultraman settings.
Also, Godzilla lost to a moth, I don't see why he couldn't lose to a cosmically-powered giant superhero.
