Oh, I absolutely “get it” and agree with your comments, but the point I was making is that *in practice* the traditional sensor in the R5 is virtually indistinguishable in tracking performance from the stacked sensor A1. I haven’t used an A1 personally, so I qualified my comment by referring to the A1 vs R5 BIF video by Jan Wegener - a very highly regarded and brand-neutral BIF photographer.
Whether the R3, R1, Z9, or Sony’s successor to the A1 improve on that tracking ability remains to be seen. Clearly the R3 (and hence R1) has faster *acquisition* than the R5 but that is largely due to the inclusion of eye-controlled AF point selection.
Certainly in *theory* a new generation (for Canon) stacked sensor should be better at tracking, as a result of faster readout, improved subject recognition and better tracking algorithms, but whether the R3, R1, Z9, or Sony’s successor to the A1 improve on that tracking ability in any significant way has yet to be demonstrated.