Maybe I'm not following correctly, but the Z6ii *does* have subject tracking. You can hit "OK" and it flips to tracking mode, put the box on an object and start tracking.
It doesn't work super well for challenging subjects, but it is there and does work.
I'm guessing most discussions in this context mean some sort of "automatic" tracking?
Yes - it's challenging subjects where it is an issue. And it's hard to access. At the end of the day, that combination means it is not as useful as the new approach with the Z9.
It seems to be ideal for subjects that are perched and taking off.