It’s not a Parallels issue, I have the same problem on a native Windows laptop. It may be related to Windows 7 though, which I’m unfortunately stuck with on this machine. The laptop has a high-DPI screen so I have Windows set to 150% text size. However, everything became larger than before when I upgraded to build 3170.
Then I connected a desktop monitor, and I’m pretty sure I saw Sublime Text enlarge itself even further, a couple seconds after I first saw it on the monitor. The monitor has a slightly lower resolution. Its DPI shouldn’t really have affected the size of anything, since Win7 doesn’t let you set it per monitor or change it without logging off.
For me, the dpi_scale setting doesn’t affect anything. I reduced font_size enough to get a comfortable text size. Here you can see the huge UI elements compared to the suitably sized text. I’d say the UI is about 2x as large as it should be. https://i.imgur.com/XqucmsP.png