Tracking birds through an evf sucks ass. Even with no blackout. OVF is still king in the widife world. One day EVFs will likely come close to matching an OVF. At least they will be good enough to not be unpleasant to use. But that is not the case yet. They still cause eye fatigue.
I don't think that coming close is all that what you call EVF will acomplish.
Focussing isn't about EVF or OVF. Using the imaging sensor vs a dedicated AF sensor is what really matters.
In THEORY, using the sensor is far superior. Period.
The sensor is guaranteed to be in the same plane where the image is captured, unlike a dedicated AF sensor, which could be off by a small distance and therefore require AFMA.
Because the focus sensors in a DSLR are exposed to light only when the mirror is in the optical path, and the light that hits the mirror is mostly used for the OVF, they can utilize only a portion of the light that would be available to sensor based Autofocus, where nothing sits infront of the sensor at any time.
And obviously, since an image sensor can capture an image, it can utilize the image content to make better decisions on focus. Eye AF is an example for this. And I think this is what the guy you responded to meant.
The thing is, making good use of the additional number of focusing points and the much richer amount of information from a sensor based focus system requires much more processing power and faster ways to read the Information from the sensor. And that is something that is difficult with small devices like cameras in general, and Canon seem to be struggling a lot with it in particular.
But they seem to push into very high resolution sensors with the rumored 100 MP mirrorless and the upcoming 32 MP 7D II + 80D replacement. Maybe they managed to get some of that under control.
If they do the same thing with the high res crop camera and the high res mirrorless like they did with the 7D II and 5Ds and just scale up the sensor, the high res mirrorless would have about 32 * 1.6^2 = 82 megapixel. Assuming they wouldn't go backwards from the 5 fps in the 5Ds, but keep it at that speed, it would be a camera with ~30% more throuput than the 1D XII. To acomplish that, they must have made some progress with their weakness.
Factoring in the size difference between 14 and 12 bit, 5 FPS at 82 mp is basically the same throughput as the Sony A9 handles with 20 FPS at 24 mp. It make me hopefull that Canon has suceeded with their stacked sensor research... But being Canon, I better don't get my hopes up.