Eh, it has always looked horrible. Non fractional scaling is just too much to ask at this point...but hey look at this tiny toggle element doing this cool liquidy effect wohoo

Only since OS X Yosemite. Then they decided to mess with the font smoothing and it went downhill from there. And no, it wasn't because of Retina, as OS X Mavericks had Retina support and still worked fine on low DPI screens.