Mr. Satan only lacks the planet-busting power of the Z fighters to actually be the hero he claims to be. He's already a pretty good character as is:
He's a loving father, doting on Videl once he discovers her existence. He's even worse with Pan.
He's actually an excellent fighter, for a normal human being. He managed to become Champion of the World Tournament on his own merits at least once, and in Fusion Unleashed he's seen afraid of but barely slowed down by the hordes of zombies in town.
He actually saved the Earth indirectly twice: first by throwing 16's head between Gohan and Cell, leading to Gohan going SSJ2, and second by ordering people to give energy for the Genkidama that destroyed Buu.
Oh, and he did save the Earth, by befriending Buu of all things. If it weren't for those two morons shooting people, the Buu Saga would have ended right there.
Despite all of his grand posing, he's a nice guy who gets along very well with pretty much all of the Z fighters except Vegeta (and Piccolo? I don't remember them interacting much)
All in all, for a fake Saviour of the World, he's a great guy and is, in his own way, a hero.