If you did manage to reduce the font size, wouldn't the quality also be impaired due to using less pixels for each font? I can understand it if you wanted to make them bigger if you had a 4k 16:9.
Basically, it's still only a 1080p monitor so the fonts will be a little large. I'm on a 2560x1080 35" display and everything is large, but then it's the equivalent to a 28" 16:9. It sits next to a 24" 16:9, but after a while I decided that the font is just too small on that one.
This may not be very helpful, but you could adjust the font sizes within your popular apps, if you can't do it within the OS. Web browser, IDEs etc.