Knew about the relationship, but am going on my own experience. I have f mount Tamron 24-70mm f/2.8 G2 and 70-200mm f/2.8 G2, 35mm f/1.8, 45mm f/1.8, 85mm f/1.8 as well as a Tamron 150-600mm f/5-6.3 G2 used on a D850 and D500 and have used them all on my Z9 with FTZII adapter. All but the 150-600mm G2 are stellar lenses. Because of the disappointing performance of the 150-600mm G2, I picked up a Nikon 200-500mm f/5.6, which performs much better than the G2 in terms of IQ, AF speed and stability. I've come to the conclusion Tamron is great at the shorter focal lengths, but not so great at the long telephotos. IF the Nikon 200-600mm f/6.3 is a rebranded Tamron (John says not, but I am waiting on confirmation) why not go with the Sony 200-600mm with the Megadap211 adapter as the lens gets excellent reviews. My 150-600mm G2 and Nikon 200-500mm zoom with the lens barrel, so they are sucking in air / dirt. The Sony is all internal focusing. Maybe I'm overthinking this, but the spring migration is almost here in SE Texas and I would really like a better quality zoom to shoot it. Worse comes to worse, I can sell the Sony for the Nikon if the Nikon proves to be a better lens, but in the mean time, I've got a solid birding lens to use in combination with my 600mm f/4G with FTZii adapter and Nikon 1.4x tele.