Its actually false to say Netflix 4K doesn't resolve to 4K, its far more complicated than that.
On static or relatively small amounts of motion, it looks fantastic. As a general rule, 2K Bluray retains a lot of finer detail that Netflix doesn't have at 4K, but Netflix DOES have clearer outlines between high-contrast areas, so it depends heavily on the scene. You will notice in their Marvel shows and Stranger Things, a lot of scenes are VERY static, bringing out the 4K detail. (not to say the 4K Blurays aren't better, I own them for Stranger Things)
What really annoys me about Netflix is their audio quality, quite a lot of movies sound really flat compared to the Bluray. I find an immersive wide sound stage can more than make up for picture loss, whereas the picture can never make up for flat audio.
It makes me sad that so many people watch TV shows and movies on their phone, laptop or even just TV speakers, because surround sound can make a night and day difference to how you perceive whats happening on the screen.