I've not had the pleasure of using an A9 and comparing it with the A7R III, but I do have two of the later bodies. Have been really impressed with their speed I must say. I suppose it's all comparable from where you have come from and the situations you shoot in.
Coming from a Canon, then Fuji mirrorless before coming to Sony - I've been really impressed with the quality, the huge files, along with the video cross over. So many features it's impossible to fully appreciate all the extras packed into such a small bit of kit.
Yes, I'd love an A9, I'd also like a few more bits of Sony kit. The old school big boys of Canon & Nikon are left in the dust. I'll never be changing back.
The animal eye AF on the A7r III works a treat for me and captures my ridgeback well, even travelling at speed, as she has no slower gearing! :-)