Here's what I don't understand. Glass says to his mother, "This was never a limited edition. This was an origin story."
Whose origin story?
The end of the movie would suggest it's the origin of a new superhero age like the X-Men simply because of belief. Glass is arguably the true protagonist of the film because he's the one that ushers this in; first by "creating" the superheroes, and then by upending 10,000 years of ignorance perpetuated by the three-leaf clover society who murders these superhumans in their infancy while covering it up. The psychiatrist insists her secret society isn't evil, but the only motivation it's attributed is envy ("it's not fair") to justify drowning a helpless man who did nothing but help people in order to conceal the truth. Seems pretty evil.
Yet there appears to be the similar rule in this movie that existed in the film Hancock. The psychiatrist said, "When one of you appears, your opposite shows up, and things escalate."
That was Unbreakable. As Mr. Glass said at the end of that film, "You know how you can tell who the villain is? He's the exact opposite of the hero in every way." Mr. Glass is Overseer's opposite. Overseer may be fighting the Beast in this movie, but The Beast isn't his opposite-- at least not in every way. The Beast is the defender of "the broken", and you might call Kevin broken because his personality has been shattered, so he is like a spiritual/emotional version of Mr. Glass. His personality is in shards. But the Beast isn't broken or fragile.
Nevertheless, this seemed to be revision intended by the movie. Glass is now a "parent". I'm guessing this is why light is Beast's weakness. Light= fire. Meanwhile, David's weakness is water.
The reason I'm confused is because there are three, goddamit, not two. Unless Glass/Beast are meant to be a hybrid opposite to Overseer there should be a fourth superhuman, already, and in the comics, superheroes have many enemies, but only one archnemesis. Three doesn't make sense. Beast didn't hurt the girl in Split because he sensed she was like him. I expected this movie to be her origin story where she would manifest her powers to counter the Beast.
Didn't happen. The most opposite character in this movie was the psychiatrist versus Glass. He seeks to create superhumans. She seeks to destroy them. He seeks to enlighten the world to the truth. She seeks to deceive the world. He pursues his goals at the cost of chaos. She pursues her goals in service of order.
Did Shyamalan not realize she was supposed to be a superhuman? Dude was asleep at the wheel.