Same specs here with massive banding and color fringes since SU5. So probably there are other factors involved (see below). Plus, different perceptions and expectations play a role in assessing the issue, because what you don’t see in many of the posts in this thread springs to my eye immediately. No offence, just pointing out the obvious.
A probable cause has been identified here:
Basically, the linked discussion involving a scenery developer shows that changes to the render engine and/or the color palette were introduced with SU5, at least in the Beta. The examples posted there show banding especially noticeable in the green and blue color gradients, and that’s exectly where I’m seeing artefacts in the sim.
Here’s textures in ver 1.17.3.0 (pre-SU5)
and here the same textures in 1.18.12. (Beta SU5)
https://devsupport.flightsimulator.com/storage/attachments/668-11820-asobo-sdk-dds-flightsimulator-svao8ykdno.jpg
(pictures by HybridNZ)