You have an interesting situation with the problems starting on previously found OK devices.
I have not experienced anything like that during the 25 years I've had this.
I also have had no success in getting a device to be OK by disabling dithering with ditherig.exe or anything else. No matter if I use polarized sunglasses, blue blocking glasses or computer glasses or no glasses or a glass of milk.
If there is PWM it is always bad, less bad with CCFL.
As for the temporal dithering or FRC, I've not yet been able to fully confirm. On a previous job I used a HP laptop that did not have PWM, but had the temporal dithering type of eye strain and when I connected that laptop to an external display, I was fine.
So for me it is kinda straight forward. Most new devices with great screens, even without PMW will cause bloodshot eyes. In that sense it is even more straight forward (or should be e.g. for doctors) as they can actually verify my bloodshot eyes. For persons with migraines it can be more difficult ans migraine is difficult to verify and is oftentimes thought to be associated with stress. This must make it more frustrating, as e.g. for me, migraine is not associated with stess, but a couple of times people have inferred that is is related to stress, though it is completely and absolutely random. I can get it on a long holiday while relaxing by the lake, or sitting in an aeroplane or sleeping.
But the red eyes are quite a physically verifyable symptom, but still all doctors try to infer that it is something psychological, while clearly it is not. Or then I have some phychological super powers as my eyes will turn red in 30 min with a display that has PWM at 99% but not 100%. My magic psychological powers are able to sense the 1% difference in brighness and absolutely without fail turn my eyes bloodshot in 30 min