system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] Why is Superman considered the most powerful person on Earth when a lot of characters can supposedly beat him?

More specifically, I’m talking about Captain Atom, Martian Manhunter and Shazam

Edit: Thanks for the great answers!
gpt
Because those characters aren't guaranteed to beat him.  Martian Manhunter \*can\* win against Superman.  But Superman \*can\* win against Martian Manhunter.  Same with the others.  But Superman was the first, so he got the title.