I never owned any old Macbooks (2010-now) and only have M1 and I would say that eye strain starts to kick in after just 40 minutes or so. What I did is that I changed color profile to sRGB to limit the color space (so it would not use fake colors to emulate P3), changed color profile to sRGB in Firefox as well (there are settings in about:config starting with gfx), disabled dock (it appears only when I move cursor on it) and its animation (as well as lots of other system animations), enabled contrast, disabled transparency. Only after all these manipulations the laptop is somewhat bearable to use.
Still it is years behind my old but still working iMac 2012 which I find the most comfortable computer to use as it does not cause any eye strain at all. Whats important to note is that I use multiple Mac OS X versions on it, each on different SSD – original 10.8 Mountain Lion, 10.10 Yosemite and 10.12 Sierra. Was thinking of updating it to Mojave but I don't like the performance, still I need it for some software that is no more aupported (and I cannot find old versions of it)