Why? Goku isn't a human, and neither is Superman so why is this needed to put them on even ground. And besides, the fact that they aren't on even ground is the whole point.
The fact that Superman Prime isn't on even ground with Goku is the whole point. Is it fair? Fuck no. Blame DC writers.
You missed the point of what I meant by even ground. I didn't mean nerfing on or the other directly to balance it out. Sure, Goku is a Saiyan. Doesn't change the fact that he's got all the weaknesses of pretty much any mammal in that it can only survive in certain environments (won't live for long in space). We take the good and the bad together. Replace human with saiyan and my point still stands.
My point is that you don't need to nerf them to put them on equal footing. However, you DO have to interpret them in a similar fashion, whether that means treating them as how they would react in such a scenario or blowing realism out of the water and having them both make the most exaggerated moves and stretching the extent of their powers tenuously. If you treat their characters and their powers in a matchup, I believe Supes (current, that is, most other ones win hands down) has the upper hand as his powers are actually more useful and he's smart enough to utilize the right combination of powers and tactics. Goku has some potent powers, but when not stretching what he can do, he's, for the most part, just a guy with a buttload of fire-power behind him. He has some nifty things, such as teleporting around, but he lacks the reactions to keep up with teleporting from each of Superman's max speed attacks and he lacks the intelligence to make enough space to set the pace of the battle. Like you said, Goku is about fighting, so he's more apt to keep the fight relatively close, in the range of current Superman at max speed and pretty much all of his powers. We're talking reasonable Flash speed attacks (not speedforce BS speed), which trumps the blur they showed in the manga/anime. Hell, if you look at their straight out strengths, that panel I posted can still be used as a reference; his strength nearly quintupled, and the image I mentioned about PLs but can't find of it breaking down his power level still had Superman pre-super cancer as having a higher Power Level. I'll post it if I can find it. Bleh.
Of course, you can reply that Goku gets stronger by scraping it out, and that even if Superman wrecks him in one clean hit he can come back to life stronger, but that's stretching what a realistic fight between them would actually entail, and I could argue that the match WAS that one bout. Then we get into the other scenario I mentioned, where you throw realism out the door and have them do stuff that they maybe wouldn't want to do or wouldn't think about doing, and powering up to obscene levels. If that's how you want to discuss the two of them, feel free, but it's not the better way to do it. It's just a different way to look at them fight.
To reiterate:
Current Superman > Goku in a reasonable test of their characters/powers.
Current Superman < Goku in a stretch of what they can/would do.
Pre-Crisis Superman/DC one Million Supes >>>>> Goku.
and I haven't really heard a good reason why this matchup can't be about the upper level Superman incarnations vs Goku, aside from dismissing it as not canon. This has the issue of different definitions of canon being possibly used, as it's clearly working under one definition and not the other. I figure it's only being dismissed because it's not "fair" to Goku.
In summary.... deal with it Goku nerds 8)