The fatigue in the case of the quest will be because there is no eye tracking, so you constantly have to turn your head to get good focus (Only the center of the screen is fully rendered), the displays are of poor quality in terms of color accuracy, screen door effect and resolution, and the lenses have a very small sweet spot. In addition your eyes have to have one of three specific IPD measurements, otherwise you are by default not in the sweet spot.

That's an interesting theory (re: no eye tracking).