This somewhat idiosyncratic topic is inspired by /r/CharacterRant.
The reason people think Superman is overpowered and not Goku is because of their respective premises.
The original premise of Superman is “what if an ordinary, decent guy was the strongest on Earth?” They kept retconning his strength higher and higher throughout the Golden and Silver Ages to keep that premise consistent through various retcons and crossovers and worldbuilding expansions before eventually giving up. They’ve restored it again in every film featuring him as well as most other alternate takes (Injustice, Smallville, Red Son etc.) Most of his villains are based on this: Lex Luthor (and occasionally Batman) is “what if the smartest man on Earth hated Superman for being stronger than the rest of the world”; Darkseid/Brainiac/Mxyptlk are “what if the strongest man met an alien even stronger”; Zod/Bizarro/Doomsday are “what if there was a villain as strong as Superman” etc. Many comics (Death of Superman, Final Crisis, Injustice) don’t really make sense without this premise.
Of course, this is a GREAT premise. But it can be a tough one to write for, and I understand why many people worry it would lead t pour storytelling.
Although I’m not big into Dragon Ball, I at least know that the premise is of a martial artist constantly training and seeking out his next and biggest opponent. This premise requires the existence of lots of stronger opponents; it’s actually closer to Batman than Superman (despite other elements like him being an alien found as a child.) That’s why some fans actually do complain that the latest series Dragon Ball Super has made him OP because its gotten harder to find opponents who could realistically challenge him.
Yes, this is the same point Death Battle made in their
most reviled videos ever. The difference is threefold: Death Battle videos are supposed to be Doylist not Watsonian, Goku could easily fill the role of “alien from another dimension who’s even stronger than Superman”, and modern DC comics continuity has in theory abandoned the idea that Superman is the strongest in Earth in favour of all the characters that are supposed to be “as strong as Superman” (including half the Justice League who are based on him.)