Explanations for Injustice

So even though Injustice is a video game, every fighting game needs to be balanced and have explanations, in this case, how can Catwoman square off against Superman ect.
Netherealm did state they will make sense of all this, even though some ppl don't care cause its just a video game.
I a'm huge comic book fan, esp DC, and lately I'm so hype for this game but can't decide which characters I wanna main or really go hard with until I know how Nightwing can fight Doomsday
Any ideas out there. I think the two health bars (armor/health) may have something to do with it.
Someone else has mentioned the possibility of Ares, god of war, having something to do with influencing the battle field but that would be stupid if he's playable. Discussions now open.
It will only be explained in the story mode. Its why Batman is seen holding Kryptonite in his render.

VS mode needs no explanation because nobody expects one. Nobody asks why Sonya is able to flawless Kintaro in the arcade ladder because logic doesn't matter there.
You should pick whoever you want to play as regardless of how the story explains stuff...

Unless you REALLY need story validation to play as a human vs a "god" in a video game where such comparisons are constantly the plot/premise.

On a side note the 2 bars of health replace the round 1/round 2 feature most fighting games have allowing the fight to continue without breaking it up and refilling both characters bars.
Yeah u guys are right Im just so hyped for this game its giving me a mind fck.
I'm aware of the 2 health bars replacing the 2/3 round system but I was just thinking maybe all the armors enhance all the characters health status to be relatively equal.
And btw chun li can fight hulk cause she out poison on her lips and gave him a bj before the fight.
It's super hero / comic book related, so there could literally be hundreds of reasons as to why the powers have shifted.
Could be anything from a stupid rage monster (MKvs DCU) or something less silly like a huge Kryptonian meteor crasheing onto Earth and Batman is using it to fight against Superman.