I would like to know if there is a non-Nikon lens where there are no Nikon alternative (where Nikon lens does not exist or is technical outperformed).
I don't care much where lens is manufactured. Many Nikon lenses are also from China or Thailand (e.g. the new 180-600 zoom is made in China....and this is a full frame lens :-) ).
Why care if the lens if from China or another country?
Personally I have a Nikon body to be able to use Nikon-glass as I find Nikon glass in most cases are superior to other brands at a price level you can live with (not very cheap but not impossible to get either).
Of course the large teles are at a price level that I can't justify to get and the reason I got the 180-600. Also a lens like the 50/0.95 is out of by budget as it would find very limited use if I had it.
A reason for a China brand lens could be that it is a lot cheaper compared to a similar Nikon lens and that the China band lens does ok (but probably not better than a similar Nikon)?
I know that there are a few examples among the Cosina/Voigtländers where Nikon were outperformed (at similar or lower price) but those are from Japan.
Then I know that there exist some very fast and quite cheap non-Nikon lenses where wide open performance is ok but not at "Nikon-level".
Then we have Zeiss-glass but not from China and not cheap.