I agree with pretty much all you said, although I disagree about there being no hope in the story.

There is a very important shred of hope in the fact that this boy did not lose his mind under the abuse, but developed a coping mechanism---his mental abilities evolved to a higher plane. In fact, his healing power suggests something distinctly spiritual, even messianic. Also he is adopted by parents who actually care enough to patiently discover what causes his behavior, something the orphanage never bothered to do. So, despite everything, I think there still is hope. It actually lies in the WH Auden quote spoken by the doctor in the third act:

The center that I cannot find
is known to my unconscious mind
I have no reason to despair
because I am already there