Monie Maybe we are twins, but who's the evil one? >=)
I only knew of the Dell U2410 because my workplace had rolled it out to the whole floor. I would imagine that a company puts a lot of research into the most comfortable monitors to stare at for 40 hours a week, every week, as to not have their employees whining and complaining constantly about viewing comfort. I liked my work monitor so much that I later bought one for home!
Your guess is as good as mine as to what the problem is. A PWM-free LED is worse than my PWM-positive Dell U2410. My guess is either an "allergy" to the spectrum of light produced by an LED, temporal dithering, or some other elusive mystery!
I don't think the Retina MBP has any PWM. Your OnePlus phone may not have it either. I also can't detect any in my iPhone 6S+ I will eventually get problems with my 6S+, and it does feel like the "LED-pain" I talked about. I also thought it might be due to the smaller screen and smaller text. However, I remember the most comfortable iPhone as being the iPhone 3G. I lost it in a Canadian snowbank once when it fell out of my phone case =(
I agree with your assessment that you seem more susceptible to PWM, while my problem seems to be something else. After losing my iPhone 3G (which I think is CCFL), my next phone was the iPhone 5, and I had to keep that phone at its minimum brightness, or I would eventually get my "LED pain" symptoms. It's the same deal with the iPhone 6S+, but if I only use it for the few minutes a day I need to, then I'm relatively OK.