On the firmware, this reminds of the days when people were harping on about Fuji's kaizen and to me that was bit meaningless because Sony APS-C bodies I had were as good on day 1 (in terms of AF) as Fuji was after 4 firmware updates!
that is not to say nikon is not doing a good job, I think they are doing a much better job than Sony actually on firmware updates.
But as a baseline having watched loads of reviews Canon/Sony still seems a wee bit ahead than Z9 on the autofocus.
Personally I would suggest buying based on the capability of the cameras today and not what is promised. camera companies break "official" promises (remember nikon DL), let alone unofficial ones and rumours of firmware updates.
I think ultimately in longer run canon/sony/nikon will all catchup to one another and any comparison in terms of AF capability will basically be a moot point.
Now if you only care about telephoto lenses then nikon are definitely way ahead IMO. for an enthusiast like me I can dream to own likes of Z400/4.5 and Z800/6.3 one day and actually use them in the field. I will never own or be able to use lenses like 400mm f2.8 or 600mm f4. And in this case I am not sure Sony will ever catchup up
But personally I also own other lenses none which canon or nikon have alternatives for - 14GM, 24GM, 35GM, 50/1.2GM, 85DN, 20-70G
I don't think Sony releases bodies as often as people think they do. They have just been around a lot longer and have a lot of lines. Each gets updated roughly on a 3-4 years cycle which isn't too bad. Obviously Sony also sell a lot more bodies than Nikon does and they also have/make more money than Nikon. So they can probably afford put out a few more bodies in general and also makes business sense to do so if they are able to sell them.
Basically if telephoto was all I cared about I would probably swap to a Z8 (with 400mm f4.5+TCs).
Overall Sony is still ahead. the 180-600mm based on early reviews doesn't seem too much of an upgrade over Sony 200-600mm which I already have. Its not a lens I would swap whole systems for.