The comics version canonically has a genius-level intellect, but I read that as raw processing power/memory, not "brilliance". That's why he can read a book at super speed and understand what the book says. So if, say, Superman and Lex Luthor were to face off in a math contest or something like that, the contest would probably be close. But Superman doesn't have the same type of creative intelligence that Luthor, Mr. Terrific, or Batman has.I'm not versed with Superman, but my casual impression was that he can with the Fortress, do some scientific stuff that is advanced in terms of technology, but that's mostly due to access or knowledge he may have?
But Luthor's intelligence is a different magnitude; he accomplishes stuff with "Earth" technology that's equal too or easily surpasses others cultures' technology.