See, that's ultimately the thing about this - Warhammer 40,000 completely outclasses every other sci-fi universe in terms of power level. The entire premise of the setting is that everything is turned up past 11 and registers over 9000 on the Holy-Shit-O-Meter.
Dragon Ball Z, similarly, exists purely to make the extreme power level of every episode even more insane than the episode before it.
The DC Universe has limits of sorts designed to sustain an ongoing, shared comicbook universe. Superman can only get so powerful before he outclasses anything any everything and invalidates the need for any other heroes and the possibility of dealing with human-centric storylines.
DBZ has no such issues. Goku is THE hero. Human-level storylines are basically irrelevant when all the relevant characters are godlike superbeings. DBZ simply doesn't need to obey any sort of limits.
Goku in basically all of his adult forms is always more powerful than Superman in all but his very most powerful form - Superman Prime. Even then, Superman Prime isn't really a valid comparison, because he's an alternate reality "What If?" version of Superman from like 1000 years in the future. Superman Prime would be something to compare to like a "What If?" Super Saiyan 10 Goku or something.
Anyone saying Superman is invincible when there's no Kryptonite involved... No.
Superman is simply super tough. There are plenty of beings in DC (Wonder Woman, Darkseid, Doomsday etc) who are easily powerful enough to hurt Superman just by punching him. These are punches that simply devastate structures in the immediate area of the fight.
And that's what I was saying earlier - the attacks regularly aimed at Goku tend to level whole mountain ranges.
Just the ambient power generated by Goku and his enemies fighting tends to be enough to devastate the surrounding landscape.
Goku is like Superman....except waaaaaay more powerful. Instead of Kryptonite, Goku simply ends up fighting more and more powerful enemies. That's the only reason he dies.
Superman's power varies depending on sunlight, proximity to Kryptonite, etc.
Goku only ever gets more powerful.
Getting his ass beat makes Goku more powerful.
Like Hulk, anger makes Goku more powerful...except it's permanent and he only gets MORE powerful the next time you make him mad enough.
Dying makes Goku waaaaaaaaaaaaaaaaaaaaaay more powerful.
Being dead is time Goku utilizes to become more powerful.
Flying on a spaceship is time Goku uses to become more powerful.
Growing back his tail makes Goku more powerful.
Kaio-ken multiplies Goku's power.
Every level of Super Saiyan transformation makes Goku exponentially more powerful than the level before it.
Just FIGHTING makes Goku more powerful...and all he does is fight.
Initially it SOUNDS like it'd be a good match up, but Goku just takes all the same concepts as Superman and runs with them like a crazy person.