I got bug reports stating that some fonts I chose look horrible on Windows. I looked into the problem, and saw that most downloaded fonts look much worse on Windows than on the other OSes. While playing with font choices, I also noticed that default fonts look decent, and I concluded that I shouldn't be downloading fonts via @font-face on Windows.
The code is also very bad programming practice. It is entirely possible that Windows 2020 will have better font rendering, or that browser providers will take matters into their own hands. If that happens, you will have to do feature detection on the font rendering engine.
Thank you for reading this far! I hope that you have found the post useful, and I'm looking forward to your questions and suggestions for improvements!