Short story short.
First of all the Z9 compares to the Sony a9, NOT the Sony a1, no 30 frames per second RAW on the Nikon, speed defines wildlife photographers and the Z9 does not come close.
Second, the current Nikon 600 4 weighs almost double the new Sony 600 f4, which I own, and shoot hand held, because it is center weighted and has a revolutionary rail focusing system which is far superior to what Nikon currently is using. The Sony professional line of camera's are weather sealed. But as I have stated many times, I do not take my equipment out in the rain. But saying that, I shot my Sony a9 with the Sony 200-600 in Costa Rica and I had no issues at all, that said, I still wrapped a plastic bag several times about the lens and camera to insulate it from the environment. Again, no issues.
Good luck and keep on shooting until the end.

Have heard back from Mark S. a few hours ago. He used his Sony equipment in CR last year for a few weeks and didn't have any problems. He also shoots a lot locally on the beaches in Florida and so far no problems. Haven't heard back from Steve P. or other bloggers I've contacted yet. Steve just did an extensive review on the A1 but no mention of weather resistance. I did notice paint chipping off of his A1 camera after only a few months use. As far as the techs are concerned they feel Nikon is better weather sealed than Sony models. I will be in Continuously damp, misty and sometimes rainy conditions for several months at a time. As a Nikon user I always felt protected from the weather. Either a camera is weather sealed or not. I have not Viewed the actual warranty and Sony did mention lite rain conditions being covered and that's all that really matters in my case. I'll just keep the equipment covered as needed so I can get the most out of it.......

Have heard back from Mark S. a few hours ago. He used his Sony equipment in CR last year for a few weeks and didn't have any problems. He also shoots a lot locally on the beaches in Florida and so far no problems. Haven't heard back from Steve P. or other bloggers I've contacted yet. Steve just did an extensive review on the A1 but no mention of weather resistance. I did notice paint chipping off of his A1 camera after only a few months use. As far as the techs are concerned they feel Nikon is better weather sealed than Sony models. I will be in Continuously damp, misty and sometimes rainy conditions for several months at a time. As a Nikon user I always felt protected from the weather. Either a camera is weather sealed or not. I have not Viewed the actual warranty and Sony did mention lite rain conditions being covered and that's all that really matters in my case. I'll just keep the equipment covered as needed so I can get the most out of it.......