Trying to figure out what has changed here. The 7DII looks just as unusable at ISO 1600 and 3200 as the 7D and 70D.
Unusable? I'd call the 7D usable as 6400 and the 7D2 and 70D usable at 12,800 at least.
It all depends on the purpose. For a small print or a internet photo, you can get away with high ISO's just fine. However, some want to print large, and the noise becomes visible, or the detail is blurred by NR.
It all depends on the person and his use.
From what I've seen, the 7D MK II is just a tad better than the 70D at high ISO, and about 2 stops behind a FF like the 5D MK III.
I'd print those 6400 files at 18x12 or 13x19 no problem. I could manage acceptable 12x8s at 12,800.