I can also get a mint Nikon 300mm 2.8 VR II for about the same price of the lens. Its not a Z lens but I have all the TCs.
I have the 300 2.8 VR II now for over 12 years, its optically 100%, just a beautiful lens in every way sharp fast accurate with stunning bokah, its sharp but has feeling naturalness emotion reality in what it delivers, used properly, its not bleedingly clinical sharp and disconnected, its micro contrast, colour detail is superb above all believable, on anything, even small birds.
It is stunning on the Z9 with adapter, especially the D6 D850, D4s D3x Df D7100 D3s D700 D300. Z7II Z6II.
Its formulae has been pivotal, the Ferrari formulae one model in building Nikon lens designs for decades and decades.
At 2.9 kg its still very usable hand held but i use it with a light small mono pod, its brilliant with a 1.4 TC III.
I use it 99% of the time at F2.8 or F4 when everyone else goes home.
On the D6 at 25,000 iso you would be gob smacked.
Yes i am bias and for very good reason.
Club members like the 100-400 lens for being light and versatile, optically they prefer the 500 pf and the 400 F4.5, even the 200-500 currently being dumped by box shifters for under $1600 AUD from $2350 to make room for the 200-600 announcement coming i assume in March.
There are some lenses a whisker sharper in the Z line up than the 300 2.8 vr II but you would need to sell the sheep station to get one of those lenses.
Its all a matter of at F2.8 its in a league of its own once you get to F8 F11 most lenses are much the same so to speak except the 300 2.8 vr II is sharp at all apitures is what i mean.
The 100-400 is a very convenient walk around lens, light and very useful, again from the birders there wanting a little more performance at 400mm
I mean a Z9 with a 50mm 1.8s lens is 1.85 kgs already.
Only an opinion