Its well known that the Z mount lenses have an edge over DSLR lenses in most cases, even more so on a Z body, where and by how much really seems to be the point to consider.
In DSLR glass i find the 200 F2, 300 F2.8, are still in a league of their own, the 105 1.4 is excellent, and especially the 70-200 FL compared to the Z version is such a close match it doesn't warrant up grading to the Z for optical reasons, at least in my applications.
The 200 F4 macro is exceptional as is the 16mm F2.8 fish eye you need to be creative to drive well.
Nikon has brought out a great collection of Z lenses.
Nikon making lenses seems to be their strength, the greatest benefits being the larger lens mount diameter increasing edge to edge performance as well as enabeling greater light gathering ability, example, i assumes this makes F6.3 seem more like F5.6 kind of thing if you get what i mean and allowes in cases also for things to be shortend.
While element formulae combinations are endless the key target of late has been on size and weight, this appeal is why many people have transitioned to the new generation of glass, add to that a 5% 10% optical gain and its considered a benefit, mind you video recording has been a major consideration as well. Smaller lighter with any product mostly reduces cost in materials, production, distribution and given the new higher prices replaces much of the margin lost of late.
The bottom line is the new glass is better in so many ways but not all cases.
Complimenting that new glass with the right body is also just as important.
Two things i find many people often struggle with, if they hang on to long before changing, the svage depreciation of the existing gear and simply the expense of the new gear often seen as excessive, well thats the word from many club members.
For years the perception has been compared to OEM lenses third party lenses are basiclly cheap and nasty and made in China kind of thing, yet here are some majors now actaully outsorcing manufacturing the very same third party maker as well as them selves producing things in China.
I do think in certain cases the Tamron range of lenses are very much on par to what Nikon is delivering and much more a consideration thatn ever before especially at the significant price difference gains, i mean i can get TWO Tamron 24-70 F2.8 lenses for the cost of one Nikon 24-70 F2.8 Z, the differnce between the two is largly but not totally........... margin
Only an opinion