I think that pure white (255) and pure black (0) should be using extremely sparingly. #FFFFFF? Why not #f6f6ef or #eceff4? Lower contrast can improve legibility, too much contrast can hinder it.
#000000? Why not #121821, a dark shade of blue? Nothing in real life is perfectly dark.
It's possible to have contrast too low, that doesn't mean maximum contrast is the best. Even HN doesn't go full black on white, the background is off-white.
Thankfully HN has remained pleasingly off-white.