That answer would be a more convincing if the page itself wasn't a great demonstration of the opposite. I'm sure #554 with a spindly font looks great on a retina MacBook, but it's just not all that readable on most systems, especially for people with less than perfect vision.

I just don't get what issue designers have with contrast. You'd kind of think that the point of text is for it to be readable, not for it to look soothing.

Eh, sometimes you don't want things to look natural for the sake of looking natural. Plus, given that there's basically just black and white on Gwern's site, a dark blue would have the same 'overpowering' effect as a black, since there is nothing else that is similar in color to it.