That is definitely not the case with the D500!
I owned the Z6 and D500 and if you are going to do videos then the Z6/Z6ii is far better than the the D500. But if it's for stills I'd still edge towards the D500 but remember switching to mirrorless you are sort of future proofing yourself. They are both very good cameras, in fact the D500 truly is a mini D5. You won't go wrong with either really.
The Z9 AF requires the user put thought into what settings are required and relying on say 3D tracking does not always work. The tracking isn't always perfect, it can move from one area of a vehicle for instance to another but trial and error sorts that out. And then you find the keeper rate is far higher and that's over my D5, D4S and D850. I think you have to get it out your head the Z9 will just nail the shots no matter what as it does not, nor does the Sony A1 or Canon R3. It's the input put into the shot that matters.
When it works it's great, when it doesn't it sucks hard. I have to do a lot more juggling of AF mode; and if you're hoping to acquire something small-ish/fast-ish in flight, good luck... it better already be in focus before you push the button (or against an easy BG and wide area large/auto selected).
I prefocus when I can, but "approximately" has to be pretty close to actually in-focus. And if the camera initially drives the focus the wrong way it's going to miss anyway.
I think wide area AF or auto area AF might be your friend here as on lots of Z9 forums/Facebook pages BIF's are the main images posted and lots of users are very happy with it. I do think it's just a case of finding the right setting. I do remember when it first came out someone saying it couldn't find birds in trees or bushes and yet I've never had an issue. It's nailed on the eye and stuck with it.
I owned both the older Z6 and before that the D750 and D500. I would say the D500 is definitely more suited towards wildlife photography compared to the mirrorless offerings. Particularly with fast moving subjects like BIF the AF is more responsive on the D500 and IMO having an optical viewfinder means there is no lag which makes for easier panning. Also mirrorless does tend to stick to backgrounds if you focus on them inadvertently. They 'needs help' with the focus ring to refocus on subjects in the foreground which can lead to missed opportunities. On the other hand - mirrorless doesn't require lens calibration to get the sharpest shots, has much more focus selection points available on the entire frame, and on the Z6ii has better resolution for cropping, and if you like bokeh, you'll achieve better isolation with the same lens compared to on a cropped sensor body
Yes, with a clean (very OOF) BG. Or if you have a lot of time to acquire the subject; once it locks on it's quite good in most modes (3D can be particularly good).
From what I can tell, the Z9 always drives the focus out initially (unless there is something immediate). IMO that makes a lot of sense in most situations, but it means I have to err towards being short when prefocusing instead of being closer...
