In a VERY dark room, I totally agree - I barely notice a difference. But even in a dark room with just "some" light (think just normal lighting conditions in your home or office), I do notice the difference. It's not like the nano-texture display looks bad at all, it just absorbs the light more I guess and makes the blacks on the screen appear more grey, and I just love the way the standard display makes those colours pop against the blacks on the OLED screen. If I'm not looking at an image with any blacks, then I probably wouldn't notice or care. If you don't care about having those deep dark blacks an popping colours (ie, if you use a matte screen protector on previous iPad's), then I think that person would be happier with nano-texture.
Agree with you that in a room with very bright light, or sunlight, nano-texture looks better.
Honestly, it's a pretty even trade off and you just have to pick what you like better... the black blacks of a glossy OLED display, or less reflections and glare.
It was the fingerprints on the nano-texture that pushed me more towards the standard glass. Ironically, the nano-texture doesn't get fingerprints as fast, but once they are there, they are harder to remove compared to the standard glass.
If you generally use your iPad Pro with dirty hands and wipe or clean the display frequently to remove smudges, I think that should be something people factor in maybe even more than the dark contrast vs. less reflection trade off. The oils and smudges really stick to that nano-texture pretty good, and I just got annoyed with that (I guess it gets all into those little holes and that's why apple gives people a special cloth - not so much for protecting the screen, more for just having something effective to wipe away those smudges).