Sports is an interesting market segment, because as Canon has made clear with the 1DX2 and 1DX3 being literally identical in resolution, their data must really show that the specific market they're targeting doesn't care about resolution.
Can't forget that Canon themselves were the first to really disrupt that market, with the R5 being 20 FPS at 45 megapixels, which was double what the "high-speed high-res D850" did at the time. They had plenty of time to consider how they would continue catering to the lower resolution sports market while making a flagship camera, and I can imagine they probably decided to spin the lower resolution segment off into the R3.
If you remove the A1, R5, and Z9 from the discussions, the R3 matching the A9II's resolution and adding 10 FPS is a pretty big deal for the people who use these.
I think there's probably plenty more for Canon to surprise us with out of the R3. Canon is really going to have to show how the R3 tops the R6 which is at least $2000 less and possibly only ~4 megapixels less. I think it's an uphill battle for that to simply be "BSI means no rolling shutter" because I really don't know how many photographers out there know what that means or looks like.
Honestly using my R5 in 20 FPS mode, I barely see the rolling shutter effects in day-to-day use, and haven't been particularly bothered by it while photographing sports and wildlife. It would be more of a bonus to me if the image quality/dynamic range in electronic shutter matches the mechanical shutter, and 0 distortion would also be nice, but I just can't imagine that being 2000-to-3000-dollars-more-nice.
One thing that would particularly make the R3 more worthwhile in electronic shutter would be making us able to fine-tune shutter speed like on the Sony cameras to anti-flicker shoot at any shutter speed and in 30 fps, which is a feature I've always wanted on the R5 and even the 1DX2. It would also be great to see electronic shutter having variable burst rates.
