At ISO 1600 and above, SNR is more critical than DR for most of us who shoot at those ISOs. That's where the 7D mark II is better than the 80D.
You can hype it all you want, but the only difference I notice between the AF system in my 5D Mark III and my 5D Mark IV is the vertical spread of the AF points. The 7D Mark II is not quite as good because the baseline for an APS-C mirror/sensor is narrower. This would also be the case for an APS-C version of the 1D X Mark II/5D Mark IV AF system. Most of the improvements between the 1D X and 1D X Mark II seem to be in processing algorithms for the data gathered by the PDAF sensor (and RGB+IR light meter when using iTR). The 5D Mark IV got the same PDAF sensor array hardware, but not all of the same processing algorithms. The 1D X Mark II AF system noticeably outperforms the 5D Mark IV AF system according to those I know who shoot with both. YMMV.
I was not hyping it in any way, merely quoting Bryan Carnahan of TSP verbatim. No more, no less. It was about the AF of the 5DIII versus the 5DIV not being the same, which was the point, not the the 5DIV vs 1DX. The AF of the 5DIII does not have the iTR that was introduced for the 7DII and is now in the 1DX, 1DXII, 5DSR and 5DIV.
Regarding YMMV, In contrast to your experience, I have used the 7D, 7DII, 5DSR, 5DIII and 5DIV extensively for bird photography and whereas the 5DSR is now my go to camera for static shots, the 5DIV is my first choice for birds in flight because its AF is noticeably the best of that bunch when fast accurate AF is required for rapidly moving small birds. You will find it repeated in many of my posts that the 5DSR is pretty competent for BIF (and even dragonflies in flight), but the AF of the 5DIV is the best for difficult shots.
My experience may differ from yours because we cover different mileage and you don’t shoot rapidly moving birds close up.
Later addition
I just remembered that Ari Hazeghi, whose specialty is difficult BIF photos, wrote a detailed critique of the 5DIV before before he went over to Nikon.
http://arihazeghiphotography.com/blog/eos-5d-mark-iv-field-review/ There is a long section on the AF, in which he wrote: "
First the good news, the EOS-5D Mark IV AF consistency is greatly improved over the EOS-5D Mark III which itself was quite a capable camera in the right hands. With the EOS-5D Mark IV, right off the bat, I noticed a higher percentage of tack sharp files with challenging subjects. It tracks very well against complex backgrounds, like the examples below." And there is a lot more. So, in your hands the 5DIII is quite capable, but for difficult BIF the 5DIV scores.