And I would not agree with your statement. The differences are getting much narrower to the point of no longer being A or b, but rather a or a'. The 1D X Mark III does not use a line sensor for the OVF based PDAF system. It uses a small CMOS sensor. This is a first for Canon. No previous EOS DSLR has used such an OVF based PDAF sensor, so your previous experience of Canon EOS DSLRs does not apply to the 1D X Mark III. Have you read what those who used pre-production versions of the 1D X Mark III are saying about it? They say it is just as accurate as Dual Pixel CMOS AF while being just as fast as previous OVF based PDAF implementations..
I'm not saying the new OVF based PDAF is not excellent and a leap forward compared to previous generations. I'm actually pleased to see the new head and face tracking via OVF.
My original post was in response to some other commenters who seemed unclear as to the distinction between AF via OVF and via Live View.
Most importantly for me, eye AF in the R series has been absolutely game-changing, and I appreciate that I can do it through the EVF. Perhaps for a large majority of the target market for this 1D camera, having eye AF through the viewfinder is not important. For me not having it is a dealbreaker. So I thought it was worth mentioning for the sake of those following along who may not have understood that. When shooting portraits of moving subjects at F1.8 or wider with tiny DoF, eye AF is positively amazing. I wish it could be done through the viewfinder of the new 1D, but it cannot.
In general, from Canon:
"Dual Pixel CMOS AF
covers a much broader area, with up to
100% (vertical) x 90% (horizontal) possible with most current Canon EF lenses. Servo AF can follow-focus on challenging moving subjects, or lock focus One Shot AF.
The same AF Area options as in viewfinder shooting are available, with the addition of a horizontal Large Zone AF setting. Set the AF Method to Face Detect + Tracking, and the same powerful Subject Tracking capabilities as in viewfinder shooting are possible.
That includes the same innovative Head Detection technology as with viewfinder shooting (to put focus upon heads, when faces are obscured, or turned away),
and adds Eye Detect AF. As a method for virtually silent still shooting, 20 FPS speed, or AF covering nearly the entire image area, Live View on the 1D X Mark III is a tool professionals can turn to."
Those to me are welcome, significant features of the new 1D series that are available, which is fantastic, but only in Live View.