Don't know where the problem comes from, but it seems logical this is on LG given the Strato works fine with the other major brands. I hope this is corrected going forward for those K owners with LG displays, but if it isn't, I'd give up the TV before before giving up my K system. Having previously placed two Sony Z9D displays side-by-side, with same settings and calibration, displaying the same movie from both sources, one displaying Apple TV, and one displaying from a Strato, you could see the image quality differences. The Strato was easily a better image.
That said, this test was done 4 months ago and Apple TV may have improved, not sure. It's also noted that these differences are not as noticeable when you're watching a single display, or watching on smaller screens. The differences are even easier to notice for those of us with projection systems and large screens.
In the end, we each find our own satisfaction levels. Many are fine with Apple TV (I did find it acceptable), but some of us continue to seek the best possible quality and currently that is still the Strato.
Jim