Eye fatigue was something we took seriously back in the days when I used to work in a publishing house.
The preference was always for a kind of paper that was matte ( the glossy paper was a no-no) and slightly yellow (you’ll pardon me, but I have no idea about the name of this paper in English), just to dimming the background color instead of lightening the type, as you said.
But there is another side of this story. If you are printing something using CMYK, a gray text will be a percentage of the black, which will result in a visible reticle, that will end up with text with blurry edges and a less defined shape compared to the full black text.
I’m not sure if this “black text” convention is more a workaround of a technical aspect or something focused on legibility.
PS: Sorry for the long text. And congratulations for the cool article!