Sports needs AF first and foremost, a super clean 25600 means little if AF cannot keep up, so in that situation AF is the most important thing.
I can shoot ISO 6400 on the 7D for sports pretty easily, I did that and marching band for years with great results. 12800 would be better, and the 7D2 should put me right there. There is no set ISO level needed for sports, each situation is different, and f2.8 at 1/1250 to 1/2000 simply depends on the lighting at hand.
IQ is just part of the equation and easily isn't the single large factor in photography for many people in many situations. IQ also isn't just ISO, yet another fallacy on the boards.
This is a shot my daughter took of the cheerleading squad last year. It prints out as a 8x10. The cheerleading squad leader loved it. It made it into their marketing material. The IQ isn't great according to standards here, but it didn't matter did it?
Not bad for an 11 year old with an SL1 at ISO 12800 with a kit lens...
Then when we glamorized it for the gals, one can see how post processing matters sometimes even more than IQ. Its a little more than I like, but strangely that is what was wanted.
So IQ right out of the camera is important, but there are many other equally or more important factors. The 7D2 will do quite well for many sports shooters, despite the rantings of diehard FFers.