Serious question: why is any knowledge of the comics (or pop culture) relevant? The argument is obviously not about comic book canon. Nobody's saying you can't write a story where Batman wins--obviously, they have (I loved the film adaptation of The Dark Knight Returns, for what it's worth).
The argument is that he shouldn't in a genuine contest that is not constrained by the need to tell a compelling story. "Superman uses his super speed and strength to hurl a building at Batman and kills him" is not an interesting story, so nobody's going to write it. But that doesn't mean this isn't what would happen if both of them were a) real and b) actually trying to kill each other.
The argument is that he shouldn't in a genuine contest that is not constrained by the need to tell a compelling story. "Superman uses his super speed and strength to hurl a building at Batman and kills him" is not an interesting story, so nobody's going to write it. But that doesn't mean this isn't what would happen if both of them were a) real and b) actually trying to kill each other.