I know Mr. Glass was there for much longer but the other 2 were never sedated for those few days they were there (did they say they were immune?).
Why even sedate the guy in the wheelchair? His weakness wasn't water or strobing lights, it was...anything. Just some metal bars would have worked. Granted, he escaped when he wasn't sedated anymore but that's not because of his super intellect, it was because of the incompetence of his captors.
They did explain it. He had almost escaped before. He was brilliant.
Your statement that he escaped because his captors were incompetent is ridiculous. He switched out his pills. When he left his room he adjusted the recordings so they saw him leave and goof off, but not that he stole the focusing mirrors from the machine for the mysterious "procedure" or that he had gone and talked to the horde.
He killed Dylan by breaking the glass in his pictures. He probably shouldn't have been allowed them, I agree. He purposely went through the tunnels to get access to the computers to arrange the video streaming.
He arranged the entire escape, manipulated the Horde and David specifically so he could reveal themselves to the world.
He should have been sedated. (though I don't agree that they should have been keeping these people secret.)
The standard was not to sedate. They could control the others. The physical arrangements of their cells were sufficient to prevent their escapes. They realized Glass was different. He was physically weak and fragile. Any physical restraint should hold him. It was his brain that was his power and that is what had to be neutralized.