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.
I think Bryan was the one doing a little bit of hyping.
Bryan's Quote from Chuck Westfall was with regard to the 1D X vs. 1D X Mark II. He translated that to the 5D Mark III vs. 5D Mark IV himself, apparently not realizing that the same PDAF sensor array hardware does not always equate to the same performance if the same processing hardware and routines are not used. I will admit that I have not used iTR with my relatively new 5D mark IV yet. My opinion may change after the upcoming fall football season.
A few paragraphs later in the same review, Bryan says: "The improved part of the 5D IV's AF system comes from the 150,000-pixel, 252-zone RGB+IR Metering Sensor. The 5D III has an iFCL (Focus, Color and Luminance) 63-zone (9x7 grid), dual-layer ambient/flash metering sensor with one layer sensitive to red/green only and the other layer being sensitive to blue/green only. "
The 5D Mark III does not have an RGB+IR metering sensor. The 7D Mark II does have an RGB+IR metering sensor with the same resolution and number of zones as the 5D Mark IV (which, apart from AF, also gives both the 5DIV and 7DII better metering in difficult lighting situations than the 5D Mark III). So in that sense, the 5D Mark IV
is an improvement over the 5D Mark III, but not necessarily over the 7D Mark II.
Much further down in the cited review, Bryan says this: "Overall, I'm very happy with my 5D IV results. I still give the AI Servo performance edge to the 1D X Mark II, but the difference I'm perceiving is only very slight. The 5D IV is performing among the best-ever EOS DSLRs. " So even he eventually acknowledges that the AF systems in the 1D X Mark II and 5D Mark IV are not
identical.
iTR was introduced with the 1D X in early 2012, not with the 7D Mark II that came out in late 2014. The 1D X was the first Canon EOS camera to have an RGB metering sensor (100,000 pixels in 252 zones with no IR) , which is a necessary component of iTR.
Further, iTR is only active with
61-point (1DX, 1DXII, 5DS/r, 5DIV)/65-point (7DII) automatic selection chosen as the
AF Area Selection Mode. Far too many users of cameras with iTR stop reading there and do not realize that in
AI Servo AF mode, the user selects the initial AF point with
65-point automatic selection . So even though iTR is available, not many shooters seem to use it. I use it sometimes when the situation warrants, but even with
Accel./decel. tracking and
AF pt auto switching set at maximum, it sometimes still tracks a little slower than I would like.