If it bothers you so much, why not just disable “Local” Dimming on the QN90A and live with the native black levels/contrast ratio?
Or, maybe return both sets and opt for a MiniLED set that has a more refined dimming zones and the correct subpixel structure.
Do note that it is not only LG OLED TVs that use WGBR or other unorthodox subpixel arrangements as this concept of an extra white subpixel has made its way over to some of their IPS LED TVs as well. So be sure to do your research.
On paper, the Hisense U9DG might give the best of both worlds, i.e. if it lives up to the hype and it’s potential in practice though.
Turning off Local Dimming and getting used to the still excellent native Contrast Rstio and Black Level of the QN90A could be a viable option. Note that some of Samsung’s older TVs have better blacks and contrast ratio due to their implementation of Ultra Viewing Angle in their newer sets.
This is what RTINGS.com had to say about the QN90A’s local dimming implementation:
It has 576 dimming zones on the 55 inch model, and the 65 inch model is advertised to have 792 zones, so larger sizes perform better because they have more control over small bright lights.
The local dimming feature in Game Mode is decent. It looks similar to outside of Game Mode, except the dimming zones look bigger and cause the entire screen to look more gray than black, so the local dimming performance in Game Mode is worse. Blooming is a bit more aggressive than outside of Game Mode, which is more noticeable. There’s less black crush, but that’s because the whole screen is just a bit over-brightened. Overall, the local dimming performs well in Game Mode. However, it’s not the best implementation of local dimming.
We experienced a strange issue where text in the center of the screen causes the entire top half of the screen to turn on all of the dimming zones. Also, we checked for the reported discoloration issue but didn’t see anything. If you notice the same things, let us know.
Apparently this TV has an Automatic Brightness Limiter:
The Samsung 55QN90A has remarkable HDR brightness. Small highlights stand out the way they are expected to, but in SDR, large areas are less bright due to the aggressive ABL.
Perhaps the newer QN95B or QN90B might fare better and have significantly more local dimming zones?