Mojave beta installed, and the fonts look equally atrocious. They are blurry, indistinct...and just bad. One of the reasons I bought a 5K iMac (three of them, actually) was to have great fonts. I am beyond angry that I will now have to sell them.
The normal UI's fonts are also worse -- about the same as the browser screenshots. Fonts are indistinct and blurry, and very light. All the result of greyscale aliasing only, I presume.