Then windows improved a lot (and I assume linux also did improve but honestly I stopped using Linux for the desktop long time ago so I don't remember) while MacOS support for low resolution text stagnated and I believe you if you say that on windows and/or Linux fonts may render better on low DPI than on a Mac.
But I have to nitpick your phrasing that MacOS hasn't been designed to run on non-hidpi: that can be right since the design is not something you just change due to neglect; a design is something that stays forever and you see vestiges of