You do raise a number of valid points, but I'm afraid you're missing the biggest one of all.
Batman is "the most realistic" because from the characters conception, an effort has been made to present him as what no other top tier superhero across any of the various comic book companies are: a human being of flesh and bone without the aid of anything other-worldly.
Superman is an alien come to Earth where he becomes a pseudo-god.
Spider-man is bitten by a radioactive/genetically engineered spider and gains mutant powers.
Wonder Woman is an amazon warrior princess, descended from myth.
The Fantastic Four are mutants. The X-Men are mutants.
Green Lantern gets his abilities from an alien race/source.
Martian Manhunter is a Martian.
You get the gist, right?
Something else makes all of these individuals special.
Batman, meanwhile, makes himself something special.
He isn't an alien, or a mutant, or anything else. While he may not be the only hero without powers he is the first and the greatest of them all.
Through discipline, training, determination, genius, whatever else... he becomes something more than he should reasonably be able to. He adds to that with his financial resources, true. Yet somehow I imagine he'd be doing what he does if he had to ride a beat-up bicycle and work out of a garage. LOL.
If you look at the Batman universe in a 100% literal context? Of course you'll disagree with Batman being 'real' -- but if you stop and realize, Batman doesn't rely on the "chemicals/radiation/genetics mutated me" or "aliens involved" to make him something beyond a man, but instead tries to show how an individual could likely do much of what is shown from him, then you realize... it's right on.
Batman is the most realistic. That doesn't mean he's got to be 100% reality. It just means, when held up against the world of superheroes, he's the closest thing to realism, even with things like batarangs and billion-dollar lives.