Yeah Nikon PF lenses is attractive due to their size and weight.Was looking at the Nikon 500mm f/5.6 PF lens and startled to find it weighs one pound less than the Olympus 150-400mm f/4.5 and is 3 inches shorter as well, likely due to the PF element in the 500mm.
Given it is about $3,300 and the 45MP Nikon Z7 II is $3,000 the combo is less than the Olympus lens alone. With cropping off the Nikon 46MP FF sensor it will be interesting to compare the two systems. My hope with the Z7 II (I'm transitioning back to Nikon, but will keep all the Olympus stuff.) is to avoid the blotchiness I see with the Olympus and maybe in their denoising or demosaicing algorithm that i did not see in my old D800E.
But comparing it to a 150-400 zoom lens that is faster its a bit like comparing apples to pears.
The Nikon PF 500mm f5.6 is also quite much smaller than Nikons 200-500 f5.6
Not sure you will get more keepers with Nikon Z7 II when shooting BIF...Z7 II can shoot up to 10fps( maybe 8fps in real world use?) but that is only with single point AF plus you get slightly lower AF performance with F-mount lenses.