What does Ponyboy mean when he says, "I was supposed to be the deep one"

While hiding out in the church, Ponyboy is amazed at how much Johnny understands the book Gone With the Wind. Pony is usually the boy with deep thoughts but now he sees that Johnny can think too.

It amazed me how Johnny could get more meaning out of some of the stuff in there than I could; I was supposed to be the deep one.

No

Yes. Sophie you slow??