Oh my. Couldn't disagree more!
I'll do my best to explain my feelings and objections, well, objectively, but be forewarned that I adore
Unbreakable and that that fact will likely color my response.
But Unbreakable really goes beyond my understanding, which I'll admit is not all that great. OK, so Mr. Glass is very breakable, but why then does he assume that someone else is totally unbreakable? That's like saying, OK, I have cancer, so somewhere there must be someone totally immune to cancer, when the truth--or at least logic--may be that we're all susceptable to cancer but some of us just haven't caught it yet!
Ah, but he doesn't assume. He wonders. He also expresses doubt about what he's doing, and indicates at one point that he'd nearly given up hope.
On top of that, we have the line from David's wife Audrey, the physical therapist, who explains to their son Joseph that when people's bodies are broken again and again, sometimes part of their mind breaks, too.
It sounds silly, but think of it from Elijah's perspective. We have a bright, articulate boy, psychologically mangled by pain and fear before even his birth...and raised on comic books. So, in his fear, and through the glasses of his love of comic books, he wonders if there's a hero for people like him. "Someone to protect the rest of us."
It's almost a religious longing, really. I'm sure you wouldn't be incredulous towards any character who reached out for a savior when life started kicking them around. In my mind, that's all Elijah's doing; he's just doing it in the only way he knows how; the way he learned by immersing himself in comic book worlds. And all his deranged plots (and significant eccentricities) go unchecked by his implied professional success (who ever heard of a poor arch-villain, anyway?).
So anyway, Mr. Glass starts searching for some superhero who can never be injured, never be ill. But to what purpose? Is he seeking a blood transfusion or a bone marrow transplant that he hopes will shift him from very breakable to maybe just occasionally breakable? And can one obtain blood or bone marrow from someone who is truly unbreakable? Is it possible even to cut the hair of a totally unbreakable person? And if you can cut his hair, draw his blood, remove his bone marrow, is he truly unbreakable? Seems the superhero can not be invulnerable, just vulnerable enough.
Nah, it's got nothing to do with curing himself. It's got to do with his purpose in life. When David discovers his secret at the end of the film, Elijah says "now that we know who you are...I know who I am."
In other words, he believes his condition existed only to spur his search for David, which ultimately benefits others. Thus, instead of being randomly cursed with a horrible disease, he is an integral cog in a larger plan. By finding David, his life turns from a cruel cosmic joke into a life of profound meaning and importance. His suffering has a purpose.
So OK, let's say we have these two total opposites, Mr. Glass and Mr. Steel. Why can Mr. Steel suddenly also read the minds of the people he encounters in the subway station so that he knows who are the worse criminals and who aren't? Is it because Mr. Glass can't read minds at all so, being his total opposite, Mr. Steel can? I just don't understand how he picks out a particular killer. And if Mr. Steel is invulnerable, how come he nearly drowns in that pool before a couple of the victims rescue him? What does that say about individual hero-vs.-non-hero abilities?
This requires a small leap of faith, I think. It's not really mind-reading...it's just a vague instinct.
Earlier in the film (at the football stadium), Elijah asks David whether or not he has good instincts for spotting unsavory types. David says he does, and Elijah asks him if he's "ever tried developing [it]." The train station scene is a continuation of that. It's not tied to his borderline invulnerability; it's just something which allows him to use it to protect others. I mean, c'mon: the premise is that superheroes are real, but not in the cartoonish way we think of them. It seems to me, then, that David's abilities are accordingly toned down.
What's worse is that at the end of this long bloody mess of mass murders in search of a superhero, nothing is resolved. As far as I can see, Mr. Glass is still Mr. Glass and Mr. Steel has given up the superhero business. I just don't get it.
Not sure how you'd come to this conclusion. I had no indication that David was going to stop saving people, and several other things were resolved. Elijah is locked up, David has accepted who he is, and presumably the responsibilities that come with it.
I don't know that any of this will change your view of the film, but I do hope it paints a somewhat richer picture of what Shyamalan was probably trying to convey.