You've gotten some data transposed. The 7DII has dual DIGIC image processors. The 80D has a single DIGIC 6 image processor. I've never used, or even touched, a 7DII. The number of image processors has no effect on AF or IQ. It does affect FPS and write-to-card (buffer clearance) speed.
I have owned the 70D. I currently own the 80D; I've had it a week.
Comparing the 70D & 80D. The 80D has more AF points, spread over a larger area, than the 70D. Moderate improvement for the way I shoot. YMMV.
The 70D could AF at 0EV. The 80D can AF a -3EV. To me, this is huge. I have thoroughly tested my new 80D with my: 28 1.8, 35 IS, 50 STM, and 85 1.8. All of them are dead-on with no MFA (My 85 1.8 requires -10 on my 1DIV). What does this mean, realistically? It means the 80D will almost instantly lock ACCURATE focus in light (0EV, 1EV) the 70D was struggling in, and missing in. It means that it can continue to focus (albeit, more slowly) as the light fades another 3 stops, well past where the 70D quits trying.
I have not tested the 80D with my zooms, or with AI-Servo. My gut feeling, from a few random sessions, is that the 80D is more responsive than the 70D.