“…severely break everything in BM’s body“
Not so much, given that Batman has superpowers; he’s just in denial. Exactly what his superpowers are very widely based on the writer, much like Superman. (No, seriously, Superman has cooking and gardening as superpowers.) Most of the time, Batman is simply super-intelligent. There’s also jokes about him having money as a superpower, which is apt, if you look at how he operates. When it’s convenient, he’s presented as inhumanly resilient to injury, and capable of healing at supernatural speeds. Such as when he took a year off crime-fighting because his spine had been severed. Then Frank Miller gave him exo-armor and prep time; and Batman transcended his mortal plane.
It doesn’t bother me because of where Batman comes from as a character. He started out as an homage/expansion of the pulp era superheros like Doc Savage and The Shadow, and their vague superpowers acquired through dubious means. So the idea that he’d be taking hits that should turn him into the world’s greatest meat smoothie isn’t that strange.
DC’s official justification is that Superman pulls his punches when he’s fighting humans, Bats included. It fits with most versions of his character. The modern dynamic of these two characters is pretty interesting, and it explains why Supes doesn’t want to kill.
Batman is a character who believes that people are inherently corrupt, and they must be terrorized into line. Either through violence, or the threat of violence. Ironically, his no-killing policy, and even his aversion to guns weren’t originally part of the character, they were added later to differentiate him from The Shadow.
Superman is a character who believes that people are inherently good. If they’ve resorted to crime or violence, it’s because they don’t see another way to solve their problems. He’s not here to turn you into a statistic. It’s about offering you a way out, and trying to help you through your problems.
Now, these are both characters that have been in print for over 75 years, so there’s some variance, but that is the overview of who they’ve become. If you’re trying to reconcile Adam West’s Batman with the one I just described, don’t, he’s actually on the Big Blue Boy Scout’s side of the spectrum.
For Batman (ignoring his personal code on killing), death is an acceptable outcome. He’s terrorizing people into line, and death is a very effective disincentive.
For Superman, death is a failure. It’s the inability to actually rehabilitate someone. So actually killing his opponents becomes a much more measured choice, and dependent on the entire situation.
Now, when someone declares they’re doing a “realistic” take on Batman, I have to laugh a bit. We’re talking about a character who, literally, dresses up as a bat, and beats the snot out of people. The more you think about it, the less sense it makes. So trying to inject him into an approximation of the real world is a losing proposition. But, this is an issue for most of the genre. Superheros function on a kind of dreamlike logic that falls apart in daylight. There have been thousands of articles, books, and comics written on the subject in the last 30 years.
But, no, Superman resisting the impulse to liquefy Batman is a character choice, and a genre convention.