But I want to use this to make a point that's a bit adjacent from Carlos' argument. I've heard the argument before from many comic fans that the reason that they find Batman cooler than Superman is that Batman is "more relatable" and "more realistic." That's an argument I've always found quite dumb, particularly from a standpoint of characterization and psychology.
When writing a character, do you define that character solely by their job? If you've never been in a hospital, do you feel that you wouldn't know how to write a character arc for someone who happens to be a doctor? If you've never worked in law enforcement, does that mean you are incapable of writing about a guy who works as a cop? Is his psychology somehow alien to you because of what he does?
Speaking only in terms of character, lets take a look at Superman vs. Batman.
- grows up in middle America on a farm in a rural community
- two parents, middle class to lower-middle class
- spends most of his childhood believing he's a "normal" human. Most tellings don't have him learn of his alien heritage until he's 16-18.
- After exploring his powers, goes to work as a reporter. 9-5 job among the other working class.
- lives in an apartment on par with middle-class status.
- Has a small group of close friends and working relationships who are "normal" civilians.
- Is generally shown to have a healthy romantic relationship with Lois Lane.
- the children of millionaires in a metropolitan city.
- orphaned at age 8-10 when his parents are brutally murdered before him. In most tellings, his childhood is said to have ended at that moment, and that "Bruce" died that night too, to be replaced by "Batman."
- shown to be an obsessive, driven loner.
- raised by the family butler, one of the few strong "civilian" relationships he has.
- through massive physical training he becomes something of a cross between the world's greatest ninja, the world's greatest gymnast and the world's greatest all-around athlete.
- on top of that, he studies criminology to a level that would put him on par with the most highly trained CSI lab techs AND a modern day Sherlock Holmes.
I note the last two because in order to achieve what he does, Batman has to devote a great deal of study to his craft, much like the dedication a concert pianist or a brain surgeon must show. Superman's powers simply turn on, so I see them as less of an element of his actual characterization.
So on a personal level, who do you relate to more? The middle-American guy who works a day job and gets along well with his co-workers, or the antisocial psychotic billionaire/Olympic-level ninja/insanely gifted detective who finds it difficult to connect emotionally to anyone?
I'm not saying Batman isn't an interesting character, but no way in HELL is he "relatable." When you read a Sherlock Holmes story, who do you relate to more? Holmes or Dr. Watson? Looking at DC's stable of characters, I'd be hard-pressed to find a hero less relatable than Bruce Wayne, save for perhaps Wonder Woman.
With everything Batman has achieved to be who he is, he's as much science fiction as a Kryptonian visitor from another planet. The comics have even carried this to even further ridiculous extremes. In the 90s, Grant Morrison had a tendency to write Batman as a cross between a Mary Sue and a deus ex machina. There was seemingly no enemy he couldn't beat by out-thinking. It got to such ridiculous levels that any internet debate about Batman versus another character seemed to end with Bat loyalists arguing that Batman would beat anyone so long as he had enough "planning time."
I recall when a cover depicting Wonder Woman with her booted foot atop a beaten Batman's head was released. Outraged Batfans argued that the idiot writer didn't know what he was doing because there was no way that Wonder Woman (depicted at the time to be second only to Superman in strength and speed, and with fewer weaknesses) could ever beat Batman.
I bring that up mostly to mention that even in comics continuity, Batman is developed in a way that makes him far more than human. The only way he's more human than Superman is physically. But when writing characters, the physical is often the least important aspect. You need to understand how they think, what they feel, what their desires are, what their relationships are.
Batman more relatable than Superman? Only if you don't give the matter an iota of thought. Don't mistake what a character does for who he is. When writing, that's an easy path to a one-dimensional character.