For some damn weird reason, DC Comics presents seemed to be the haven for philosophical and existential Superman comics in the 70's and 80's, while the main titles were mostly plodding around with generic plots and bland badguys. There's several issues, such as this one, Starlin's J'onn/Supergirl/Spectre/Supes arc and Gerber's surreal final issue. I guess DCP was considered "experimental" enough that stuff like this could be snuck in.