It does actually.
*social statistics major powers activate!*
If I'm using a measure such as gamma or phi to test if a pattern is occurring, I don't just use the percentage of DLC characters who are top tier in a vacuum, that percentage is graded based on the relative percentage of other all samples.
Basically, I would be doing what is called PRE or "Proportional Error reduction" that is "How many fewer mistakes do we make if we take a pattern into account?" If we make a certain amount of fewer mistakes or more, based on a given alpha level, we can assume the pattern holds based on that Alpha level (a traditional Alpha level is .05, meaning "with 95 % certainty")
So let's say we have a top 10 list.
IF we assume that a DLC character has a EQUAL chance of being top 10 as a non-dlc character, we will have the following top 10 (also, we will be using the status of the DLC characters AT THEIR RELEASE because this is when most are bought):
24 starting characters
6 dlc characters (scorpion, lobo, zatanna, martian, batgirl, zod)
Easy division here. There are 4 times as many starting characters as DLC, hence we can expect 4 times as many vanilla characters as DLC characters in the top 10.
Expected percent for vanilla: 80% top 10 occupation
Expected percent for DLC: 20 % top 10 occupation
Given Scorpion (on release), Martian, Batgirl, Zod are top tier:
Given percent for vanilla: 60% top 10 occupation
Given percent for DLC: 40% top 10 occupation
The only thing preventing me from turning this into a decisive PRE measure, is the small size of the sample. Even if I included the MK characters, I would be about 30 character samples short of getting a good gamma.
HOWEVER assuming the next game follows the same pattern as Injustice for the top 10 measure I listed above. I would conclusively get a gamma that refutes the negative hypothesis at a .05 alpha level, and could say with 95% certainty the following:
"DLC characters are more likely to be top tier then non-DLC characters by virtue of them being DLC rather than vanilla"
So balls in NRS's court on this one. If they release another game with DLC characters as far above the roster as they are now, I can litterally, mathematically prove my point (with 95% certainty due to alpha level)