Coming from M-4/3 I'm used to 20MP, so 33 is a pretty good step up for me. I can tell you the AF on the A7 IV is incredible. It finds eyes and locks on fast, it finds birds animals and people and locks on, and it does it in video too, if you shoot video.
We have a pretty large congress of turkey vultures in the neighborhood, we've had as many as 60 overhead at one time with 20-30 being normal when they kettle in the evening. I have stood out there in years past and shot hundreds of photos to find only a handful in focus. The camera would hunt and hunt, sometimes never focusing on anything. I recently went out on one of the rare decent days we had and shot a bunch of photos with the A7 IV and found only one or two not in focus.
Yesterday I bought a nice used R III to use as a backup. I don't expect the AF to be as good as the IV since it's a few generations back, behind the R IV and the III, but am not all that concerned. It'll be fun in APS-C mode with the 200-600 for birds at the feeder and 18MP images as opposed to the <14 from the IV.
I didn't move toward Sony for IQ or MP, I was perfectly content with what the G9 provided. I went to Sony for AF, and since the IV had the latest and greatest (same as the A1 but slower sensor read) it was my target. If top-drawer AF is your goal, get the IV. On the other hand if you want/need the crop advantage offered by 60MP, then the R IV is the choice.