It is an amazing piece of kit. Especially now that you can get a good used price on the body and the lens is probably the best value for performance you can buy for wildlife. The AF in my opinion still bests Canon R5 and Nikon Z9. The only thing it is missing compared to those is the Bird Eye AF but it does have the Animal Eye AF that works on a lot of different species (I've had it work on deer, raccoons, seals). Yes the A1 takes things up another notch but for 95% of wildlife shooting the extra performance of the A1 probably doesn't even matter.
I would also consider picking up the 1.4TC as on the A9 with its 24MP sensor the 200-600/1.4 still provides a really good image (on the higher MP A1 I prefer to crop the bare lens over using the 1.4 but on the A9II I liked using it when light allowed (f/9) and 840mm was needed).
I ran my A9II in Tracking Sensitivity 1 and mostly kept my lens on OSS 1 or OFF for really high shutter speeds and erratic birds like swallows IF.