Well, in Dragon Ball Z, power levels are measured in a more straightforward numerical way. Goku at his Super Saiyan levels has an extremely high power level. In the Justice League, Superman is one of the most powerful with his super strength, heat vision etc. In a fanfiction, you could say that Goku's Super Saiyan Blue form might be on par with Superman in terms of raw power, but Superman has other abilities like flight and x - ray vision that Goku doesn't. So it's a complex comparison.
Well, in Dragon Ball Z, the power levels are extremely high and can reach planet - busting levels. Naruto's power levels are more focused on ninjutsu and chakra control, which are not as astronomically high but still very effective in their own world. Highschool DxD characters' powers are more about magic and their devil or angel forms. So, it's hard to directly compare them in a simple way.
One interesting fanfiction could be about a human character discovering a new form of power that is unique to humans, not Saiyan-based. For example, a story where a human martial artist figures out how to tap into the latent spiritual energy within all humans to achieve a power level that can rival the Saiyans.
Training is a key factor. In fanfictions, humans can train in extreme environments, like on a planet with high gravity. This forces their bodies to adapt and become stronger, increasing their power. Just like how Goku trained on King Kai's planet.
Some authors look at the power levels in relation to the story's plot. If the story is about a character trying to save a dying universe, they'll give that character a power level that's just enough to face the challenges ahead. They might also factor in things like the character's willpower and how it affects their power level, so a character with a strong will to protect might have a power level that suddenly spikes during a crucial moment in the story.
Well, consider Goku at his peak. His power is so immense that he can shake entire universes. In Star Wars, the most powerful Force users can move objects, influence minds, and have great combat skills. But compared to Goku's Super Saiyan Blue or Ultra Instinct forms, they seem relatively weak in terms of pure destructive power. But the Star Wars side has things like starships and advanced weaponry that could potentially level the playing field a bit.
Dragon Ball Z is both anime and manga. The anime was adapted from the manga and they share the same story and characters, but presented in different mediums.
In some fanfictions, Devilman's power is on par with the early - stage Dragon Ball Z characters. For example, his physical strength and speed might be similar to Krillin or Yamcha. But as the story progresses, he has to face more powerful foes like the Saiyans. His power is more of a dark, brute - force type compared to the ki - based powers of the Z - fighters.