I just want to say, that I don't understand some people. Tier lists are opinions. That's what they are at the core, there can NEVER be a list that is 100% objective or one that is a fact or some sort of law. This tier list obviously holds more weight than others because two of the current best Injustice players (based on tournament performance) are the ones who devised it. With that said, it is still entirely their own personal opinions, it simply cannot, and will not, ever be different.
Tier lists are estimations of value. You're estimating a characters value, from their tools and their match-ups, to their viability and versatility. And what you have to understand about value is that it is, and can only be, subjective. So, after you've asked why a certain character is placed in a certain tier, and after you've been explained to based on the criteria I mentioned, at the end of the day, it will ALWAYS, ONLY, EVER... come back to, they just are. They just are because it's a subjective evaluation based on personal experience and knowledge.
Please stop acting like tier lists CAN EVER be perfect or "right". The only thing we can ever possibly do is make them as accurate as we can, and even then, not everyone will agree 100% on a tier list at any give time, because... tier lists aren't and can't be objective.