But this applies to a hell of a lot of comic book characters. Comic book writers are clever and can come up with solutions in advance to any problem the villain throws Superman's way. This can make Superman look clever enough to come up with really smart plans at a moments notice. But again, insert fictional character here. It's not part of Superman's character to be that smart, he involves himself with a fair bit of science but in any good Superman story he uses other scientists as consults.
What I feel is a pretty accurate list of the smartest men in the DCU;
5. Gorilla Grod. I'm counting him as an earthling, but also his whole concept is to be mentally dominant over man.
4. T. O. Morrow. In a room full of his super science peers, only he had the tactical genius to take down Black Adam.
3. Lex Luthor. This guy is smart enough that he has actually gone through most of life without ever working hard. He saw the greater profit in marketing the work of lesser scientists. But when he has to get his hands dirty, he will learn any super science on his own.
2. Mr. Terrific. His super power is being the smartest man in the world. And even he thinks that he isn't as smart as,
1. The Atom. The man just knows everything and pulls it off believably.
Batman is not one of the smartest DC characters, he is very smart but his claim is to be being the world's greatest detective.