The best thing about the original Injustice was the fact that, in the climax, the "real" Superman came to the Injustice universe to kick evil Superman's ass.
That didn't happen in the sequel, and instead we got a full game with evil Superman as the only Superman and Batman kicking his ass at the end.
Now, this is really problematic not only for us as Superman fans but for the image of the character in pop culture as well. This is one of the few videogames based on DC characters and featuring Superman we're getting. There's a game with Superman coming once in a blue moon, and when it comes we have to deal with the fact that it has a total misrepresentation of the Superman. And videogames are a massive medium. Much more than comics, that are niche. People who read comics are a very small minority. Most people get known these characters through movies, TV shows and videogames. For many people, this is the only thing they know about DC. Superman's popularity has been dropping for years, and this portrayal is poison for the character in pop culture.
So, given that this is the only fighting game featuring Superman that we're going to get, I propose a writing challenge: Imagine you had to introduce good Superman again in a potential Injustice 3 and make him central to the story. How would you do it while continuing the same storyline that was established in the previous 2 games?