Nikon's reputation for backward compatibility rests on a single decision in the mid-80s when AF appeared and a lot more electronic communication was needed, and Nikon decided not to do what Canon did in 1987 and change its mount. Whether Nikon's was a choice to favour backward compatibility over electronics or backward compatibility was invented retrospectively as the excuse for a dumb mistake I don't know, but I suspect the latter is more likely. 

I have never seen Nikon advertising that made or implied a guarantee of backward compatibility. In the 1990s, soon after Canon had spectacularly trashed backward compatibility, Nikon advertising made a point of saying that any F mount camera could use any Nikon lens made after 1977. But it was and has never been a major selling point because then, as now, it was innovation and new features that sold. Nikon's Press Release for the D1, eg, has 500 words on sensor, exposure, 4.5 fps etc, etc, and 13 on backward compatibility:  "Its innate flexibility allows D1 to accept more than 80 Nikon F-mount lenses"; in the D3 press release there is not a word about backward compatibility; in the Z system press release all it says is "the new mount adapter will enable compatibility with NIKKOR F mount lenses".

In the digital era backward compatibility has been the exception rather than the rule. The vast majority of the dSLRs Nikon sold - D5600, D5500, D5300, D5200, D5100, D5000, D3500, D3400, D3300, D3200, D3100, D3000, D80, D70, D60, D40, and D40X - are not AF-D compatible. On the same list of cameras, Ai lenses can be used but exposure is manual only. Backward incompatibility of new lenses with cameras even a few years old was usual, even at the high-end: E diaphragm lenses, introduced from 2014, won't work on a D1, D2, D100 or D200, made until 2007; AF-P lenses, introduced in 2016, do not AF on F6, D1 series, D2 series, D40 series, D50, D60, D70 series, D80, D90, D100, D200, in the case of the DX lenses D300 series (made until 2012), D700, D3000, D3100, D3200, D5000, D5100.

Regarding backward compatibility Nikon made the decision to keep its mount and seemed to be right then as Canon was initially struggling with EOS mount and the ultrasonic motors. Here it seemed to offer a smoother transition to support both in Camera and in lens AF-motors like Nikon. Tide changed when F4 still hat one AF centerfield and even more important when it took Nikon years to provide fast Supertele lenses (and still AF-I fist) at a time when Canon provided IS (a technology where Nikon originally was pioneer). These years in the late 1980s were the times when Nikon lost the pros (and did not regain this leading position until now. Nikon never was leading in overall sales, always had the third position behind Minolta and Canon there. Becoming second in the early digital SLR era and after Minolta has faded away was a new situation.
Coming back to compatibility Nikon keeping the bayonet saw itself forced to make two vast changes (G lenses and then E-lenses) to finally bring communication to fully electronic which in hindsight might lead to the thought that a radical change might have been favorable (finally Canon had to change mount again with mirrorless and so did Nikon)
You described the lack of compatibility throughout all these changes, especially with beginners models,  but for  a long period of time when you bought in high-end cameras you got more (but still notunleashing the full potential) support. BTW when G-type lenses were announced Nikon pretended that this is not a general change but just another option for cheap beginners lenses - until the release 70-200/2,8 showed that Nikon in fact had other aims.

It is the combination of an action camera with a higher pixel density than FX that made it for me and many other nature photographers. A true D500 equivalent today would be a 40MP DX camera with Z8 capabilities, and personally, I would preorder it, even at Z8 pricing.

If you have a 400mm lens you have to be 22m from a 2m lion to fill the FX frame - get 45MP on the lion with a Z9. On DX you can be 33m away and fill the frame - with your hypothetical camera you get 45MP on the lion from further away, or at the same distance you can use a 300mm lens instead of 400mm and save some money. But with an 800mm lens and a Z9 you get 45MP on the lion at 40m. So, if you can be confident of getting within 40m and you have an 800mm lens on your Z9 you don't get a pixels-on-target advantage with DX.

That means you also have to factor in the quality and availability of very long focal length lenses and how well target recognition and tracking AF utilise them. Z has turned this upside down. The AF-S 800/5.6 cost US$16K and sold 3.8K between 2013 and now - effectively up to 2018. The Z 800/6.3 costs US$7000 and has sold 13K since 2022. In Z mount, a lot more people can afford a lot more reach.

Of course, there will always be occasions you can't get close enough, whether because the animal is too small or too elusive, but the pixels-on-target advantage of DX in the D5/D500 days has been eroded in Z mount.

A nice portrait of a common subject.  Small birds are hard to get right I think - move too dammed fast and their size works against getting big images.

Gracias, thank you Hugh, Bruno, Frank, y John

The Minolta 7000 Maxxum had Focus Priority AF so even if the lens was in focus if the camera didn't detect sharp focus you could not take your shot. I found the Minolta 7000 Maxxum's AF useless. I spent a few minutes with the 7000 Maxxum at Gayson's Camera in Glendale, CA lost all interest in the camera.

Let us hope that it was a momentary lapse.