That matches what I'm seeing online from others and my own experience. I just got my A7rVI a bit over a week ago adding to my stable which includes the A1ii and A9iii. Clearly, the changes in this model:
Vastly improved viewfinder .... ie - brightness and color accuracy
Better battery
and what helps that battery - single merged chip for AI and processing using much less power
Compressed HQ - a lossy compression where the lossy-ness is only applied to the low detail areas that won't care
10 easy to access Memory slots for different camera setups (* on the top dial), 10 each for photo, movie, and s and q movie
The dual mode sensor readouts combined in single shots or movies to increase dynamic range (making this great for landscapes and still pretty great for BIF)
These combination of features will now be in each new camera that comes out. I'm very excited to see what's coming in an a1iii and if that's a global shutter, the A9 niche will vanish.
What has surprised me, of course, in the past my A7rV was pretty useless for BIF with the blackout viewfinder making my own tracking hard and the cpu losing AF input as well, is how well the A7rVI does with fast subjects.
I assumed it be pretty useless on humingbirds, but it did fine this week when one showed up with very little wing distortion. In fact it was very dim lighting deep in the woods and it was darting almost randomly to whatever it could find. The a7rvi still picked it right up and locked on the eye easily outperforming that initial acquisition compared to either of my other cameras.
Dragonflys in flight, of course, were still a mess with the even not bad rolling shutter, but they are mess even on my A1ii so no surprise there. All or great on the A9iii.
I guess, what surprises me is how much of how I use my A1ii is actually just fine on the A7rVI or even better than fine. Eyes on great herons clear across the pond where I shoot nearly daily immediately pick up on the eye where neither the A1ii nor A9iii will do so.
As far as refresh rate on the viewfinder when shooting high FPS, I'm not that concerned with it. Simply having it bright enough in bright sunlight birding without having to wear a hat with a visor arleady puts it way over my A1ii or A9iii in my mind.