Well, of course it is of lesser utility. It is the hammer principle - when you have the biggest gorram hammer around, screwdrivers really cease to be useful to you.
No, you can't. Because in calling him underpowered and mundane, you have thoroughly under-stated Batman's prowess, and your game system probably isn't built for modeling him properly.
Batman, the Flash, Wonder Woman, Green Lantern, Superman - they are all gods. Now, approaching this as a D&D/Hero/GURPS atomic action simulation player, and primarily basing action on "the character knows what they player knows", you are going to run into trouble. Why?
Superman is strong, sure. He can fly in space. He's nigh invulnerable. But Batman has the
GREATEST ANALYTICAL MIND ON THE PLANET. He has one of the largest fortunes on the planet, and technology not seen in anyone else's hands. Did you model all that properly? Or, were you worried about how hard Batman can punch?
Did you note that Batman really should have hooks into satellite detection systems so that if the Red Son comes to drop a rock on him, Batman has known for an hour and a half? No? Then you have failed to understand Batman. Batman lives in this world 24/7/365, and sleeps for 15 minutes a day, and then only lightly. Your player does not. Batman will always know more than any player at the table. Batman knows more than the GM. If your Batman does not have a power equivalent to, "I know things before anyone expects me to know them", you have not modeled Batman properly.
I submit that any primarily action-resolution based system fails to understand comic books. Task-resolution games give us, in effect, a sort of game-world physics. Comic books
do not have consistent physics! Comic books are a media in which Squirrel Girl, with the proportional strength and agility of a squirrel, can defeat Galactus off screen, and have that be satisfying! Because, at their root, comic books aren't about action resolution, so much as they are about
conflict resolution. A system like Fate or Cortex+, which is less about what the character can do as a physics model, and is more about who the character is in the fictional world, is a far better match for superhero play.
I take it you have little or no experience with the Cortex+ based Marvel Heroic Roleplaying? The game never went anywhere because it failed to come up with a good character generation system. However, if you look at the official characters there... yep, you have the relatively mundane Daredevil and Hawkeye able to work quite successfully alongside Thor and Iron Man, despite what seems like a power differential. The "plot armor" isn't in the form of a special separate luck ability. It is in, for example, how Captain America is basically the best tactical leader on the planet - such that when he's working with a team, anything he tries to do with that team has the same weight in the fiction as getting punched by Thor.
Right. So, why are you modeling them with a game in which, "Are you going to die?" is a mechanical question that you have to worry about? Why aren't you modeling them with a game in which that is a question of fictional positioning and dramatic appropriateness?
You worry about "plot armor" because "plot armor" is a patch to a physics model to make up for its lack of ability to do what the genre asks of it.
This is why GURPS Supers stinks.