I don't see how that is true in the slightest. The Z9 is a true flagship that stacks up well against the competition. Cameras lower down on the segment stack can also hold their own, albeit some would argue the autofocus is lacking. Autofocus is just one piece of the tech in a camera.
A lot? This must mean you get your info from Youtube grifters. Every serious reviewer has praised the Z9 for having world class auto focus capabilities that defy belief. People are panning tiny birds in flights and it just keeps hitting it.
The only criticism is that Sony has a tiny notch up in very specific situations, yet that gap is rapidly shrinking. We're talking really marginal differences here.
The annoying thing is that Sony simply cannot do software. I love my A7S2, the hardware is excellent even years past its release, but the menus are confusing as fuck, why does it even ship with WiFi with the option to connect it to an existing network when their own software can't detect it there, or why does it need yet another piece of proprietary software to be used as a webcam instead of just implementing USB UVC...
Battery life is much worse but when you go all in on next gen Mirrorless cameras there are gains that are just impossible otherwise in a DSLR. The thing that convinced me was using an A7RII 5 years ago in NYC at night. The simple fact of the matter was that the camera could focus and validate setup in the dark better than my own eye with my personal Canon DSLR, even with the wide open nifty 50. I think we are on the edge of major innovations in camera tech. The size advantage makes it easier to carry more batteries as well.
Really the biggest thing is that Nikon is just brutally behind in tech compared to Sony and even Canon. The market has moved past DSLRs. Sony showed up and showed how to do it and that was it.