It's a matter of perspective. Peter Parker comes from a lighter universe, and in that universe he uses Spider-Man as an outlet for himself. Peter not only feels it's his responsibility to be Spider-Man, but he enjoys being Spider-Man... I'm limited in my knowledge of the comics, but I did at least observe in SM2 that when Pete was looking for his escape, it was because his life as Spider-Man was overlapping with his life as Peter Parker, to the point he didn't have time to embody his alter ego and accomplish what he wanted to in his dual life.
The conflicts are exactly the same as with Batman. Whereas Peter does often enjoy being Spider-Man, he does it out of need and obligation not for thrills. You mentioned Spider-Man 2, and in that he turned his back on Uncle Ben in that dream sequence. The very person who was the reason he became crime fighting Spider-Man in the first place. It wasn't Uncle Ben that made him come back as Spider-Man. It was the need to be Spider-Man when Doc Ock abducted MJ.
There was no anguish or stress being taken out on him like in Nolan's Batman trilogy
If you ignore his guilt of his Uncle's death, his isolation from MJ, his best friend blaming Spider-Man for the death of his father, failing college, losing jobs, unable to help his poor Aunt with her mortgage on the family home etc....sure his life was a bed of roses.
and more importantly, Spider-Man is a much younger guy and in a universe where he has superhuman powers.
What relevancy does that have? Is Peter any more immune to feelings and emotions than Bruce? No. It's got nothing to do with age or super powers. Peter feels anger, guilt, emotional pain just as bad as anyone.
Heck he is Spider-Man because he feels responsible for Uncle Ben's death. Being able to climb walls and shoot webs doesn't make your heart stone or your mind stress free.
Same goes for Superman. I hate to draw out the 'realism' card, but it applies here because with this Batman, we're seeing injuries, scars, his own health being afflicted, and a Bruce that clearly never intended to be "Batman" forever. Given the conditions, I don't think it's ever possible for Bruce to embrace the Batman persona on anything other than pride and virtue that goes beyond what's reasonable for a human being.
The realism card like your point about age and superpowers is not applicable. Bruce suffering injuries is no different to Spider-Man or Superman suffering injuries. All three Spider-Man movies ended with Peter looking like a battered up rag doll.
Flesh wounds heal. Emotional wounds....that's another story. Batman could take a bullet wound and not give it a second thought. Failing to save Rachel from blowing up....not so easy to heal from.
Conveniently, you missed out the key line "I hope it does."
Not conveniently, it was deliberate. What does Rachel's hope of Bruce getting to be normal some day have to do with her belief that it won't happen?
I hope world peace comes some day but that doesn't mean I think it actually will.
You're right though, she does say she's sure, but she doesn't have to be right and there's still a slim chance that he can get over Batman, given the context.
She doesn't have to be right, but it adds to the other messages given in TDK about Bruce always going to be Batman and it's obvious what Nolan was saying in the movie's narrative.
Then there's the obvious plot of Bruce banking on Harvey taking the reigns for him as Gotham's hero and look how that one turned out.
What could Nolan be trying to say with all of this?
I'll give you that, it's there. But what does it mean anymore? That Joker exists off screen now, and we'll have no idea what becomes of that line if anything.
Whether Joker was in TDKR or not wouldn't change the meaning of that line because showing one more battle with Joker wasn't going to show them in a life long battle was it?
Batman has faced Scarecrow twice so far, but that doesn't mean they're in it for life as enemies.
What we do know is that Christopher Nolan is planning an ending, something much more conclusive than what we got in Begins or TDK... so will Bruce maintain the status quo? It's possible, and it would validate Joker's line, but on what this movie is about, this is what Chris Nolan had to say:
You can interpret the quote how you wish, but the way I do is that Chris is saying in spite of what the Joker said, Batman is not locked in this battle forever. They're hearkening back to finding the reality in these films, and they're going to give it a conclusion that truly ends Bruce's journey as opposed to implying it will go on endlessly off screen. You and others may do so differently, which is fine, but just so you see where I'm coming from this is what indicates to me that the direction will be ending the journey, along with all the rest of the emphasis in the marketing on this being the closing chapter of the story.
I've seen that Nolan quote about the 'conclusion'. Saying these things don't go on forever like in the comics doesn't necessarily mean Batman stops being Batman. He ended both of his previous movies on a cliffhanger/loose end type ending. Begins had the talk of escalation and the revelation of the Joker card. TDK had Batman wearing the rap for Two Face's crimes and getting chased by the Cops.
Both of those movies left the audience feeling there was more to come. Having a conclusion doesn't mean Batman's going to hang up the cape.
A career that spans decades upon decades as Batman without dying or becoming a paraplegic.
The narrative of the stories is not decades upon decades. it's spaced between several years. A year's worth of Batman comics in continuity can have happened within three weeks in Batman's world.
And when his back was broken in the comics by Bane, it was by paranormal means not present in the Nolanverse that allowed him to return iirc.
Which is why his back will most likely not be broken. Same as how Ra's Al Ghul is not coming back after a dip in the Lazarus Pit.
Aside from how much screen time it would eat up having Bruce bed ridden with a broken back, and there's no way Gotham could be left under Bane's rule for as long as it would take for Bruce to recover from an injury like that. This isn't Knightfall where he has a Dick Grayson or Jean Paul Valley to take his Batman mantle while he's recuperating.