Markus This lends to my theory that this whole issue is solely pixel movement/rendering.
The wiki for VNC shows it uses the RFB protocol - "Although RFB started as a relatively simple protocol, it has been enhanced with additional features (such as file transfers) and more sophisticated compression and security techniques as it has developed." Although it may not be using PCoIP (1-1 pixel data as the host) it may be using some form of lossless compression.
Also as you mentioned, setting up a 'good' OS as host doesn't cause you issue, but a 'bad' OS does.
I've recently got a new Dell U2419H - after using it for over a month including two weeks on my known good machine, I can confirm it's 100% comfortable for me to use and I've had no ill-effects. I can rule out LED as the culprit too, as well as PWM to an extent.