You did make up a superhero that would throw people through windows. I'd rather see a Defenestrator movie before a made up Will Smith super hero movie. The only reason no one will cast Will Smith as a real superhero is because he'd crap up whatever property they gave him.
Let's see... Wolverine "NOW THAS WHAT I'M TALKIN' 'BOUT, bub." Nope that wouldn't work.
Cap? "AVENGERS ASSEMBLE AND GET JIGGY WIT IT!" Dear god no.
Dr. Strange? "By the hoary hosts of Hoggoth, parents just don't understand!!!" hmmm... funny, but no.
Batman? I'm not going to even bother coming up with quote for this one because he'd probably make it a contract stipulation that that horrible son of his be cast as Robin and crap it up that way. My only prayer at that point would to have Heath Ledger rise from the grave and beat that little bitch to death with a crow bar like in the "Death in the Family" story line.
Superman? "...He stands for Truth, Justice, and WILL 2K!!!"
My overall point is that Will Smith turns anything even related to an action film that he's in to schlock. He only has two modes while acting. Decent dramatic actor, and complete and total fucking ham. I'm convinced that he could not do a superhero film without inserting to many corny ass jokes... I mean it, there literally is a corny ASS JOKE in Hancock.