I would say Injustice, if only because almost every major area of the map had, at one point or another, someone placing that was new to that level of play from MK9. That was a tremendous time, filled with a lot of fun drama and hot competition. Evo 2014 will go down as one of the great tournaments in NRS history. Huge upsets, long matches that went down to the wire, and the beginning of the era of Sonic Fox. Great, great stuff.
Injustice does have an unfortunate legacy of being the second game in the company's catalogue, so it started the has-beens of the scene to start acting up, which sucks. The trend is far worse in MKX, but it has its ugly roots in Injustice.
MK9 and MKX had great moments, but I would argue one of the unfortunate things was that the competition really bottlenecked at a certain point in both games. The level of play was always fun to watch, but it was largely the same dudes battling it out for supremacy. At some point during the games you would still have that moment of "woah, that was a great move" occasionaly, but it was still mostly the same dudes. This isn't an actual problem, but as a viewer it can probably get boring. Injustice had a revolving door of usual suspects, with only a few really consistent placers and always some sort of little surprise waiting to happen.
I don't really have delusions when it comes to general mindset; way back when, people still pined for "one more patch" and of course, nothing would actually assuage their tastes. The only thing that's happening now that is different and ten times as harmful is people sort of passive-agressively trying to discredit the game as a whole, thus making one's accomplishment in a particular game as less meaningful.
That's the kind of crap that is truly toxic and anyone involved in that should be ashamed.
Last thing I'll say is I do truly believe Yomi was a detriment to the regional scenes as a whole. The NRS scene of players is still a burgeoning one, and with such a small playerbase it is ill advised to rake up all the top talent because then all it does is leave those very small scenes without access to their best player(s), thus deflating the potential talent that could have come out of that region. I'm not saying those regions didn't have their own issues (California home base fluctuating, many of the GGA guys entering the industry, those New York guys just kind of evaporating into thin air), but I think taking the best players away compounded those issues even more.