Mainstream Superman is amped by prayer too, that's why he was able to cut the Phantom Stranger.
Or did the prayer allow him to physically interact with him? Not sure.
But injustice superman's feat leaves a lot to be desired.
For example,
Mogo is a planet sized being with the will power to match but he can't survive the sun? Mogo should be able to survive a star right? Since he couldn't, how powerful is he?
Being a superman fan i would like to think that superman had defeated mogo and the sun just took care of the rocky planet, but I don't think that is the case.
I think treating Ganthet like a nobody is a bigger feat.
They are basically the same person with 1 bad day seperating their morality. Injustice SM wins due to his willingness to go all out a lot quicker N52SM. Add the fact that Injustice SM has a Fear powered ring he wins this hand down. Finally Injustice SM took down a Guardian and pushed a planet IIRC over 10X the size of Earth into the Sun blows away regular SM feat of bench pressing the Earth.
I think normally Dcnu Superman would get stomped without a sun dip but with one he should win I believe the feat shared with J'onn J'onzz was more impressive than the Guardian and Mogo feat which just shows how feats have become. Anyway I believe Nu Supes still needs oxygen so that could be the ultimate problem even if the scales are balanced. Ring wearers do not have to worry about oxygen in space to say the least.