Have you tried to use the windows ClearType Text Tuner to improve the font rendering? Windows tries to take advantage of subpixels to improve crispness but it can cause color fringing which makes text harder to read. The tuner utility helps with that. You can also disable cleartype entirely to get standard anti-aliasing, which is what macOS does on non-retina screens. Personally I find the macOS way of rendering on standard dpi displays a bit too blurry.

As for images, the only difference I can imagine is a different handling of color profiles.

Update: I totally forgot about the mixed dpi situation. When you hook up a monitor of a different dpi than the laptop (e.g. the laptop is 150% scaling but the monitor is 100%, or vice versa), then only one display will be perfectly crisp for all apps, and that's the primary display at login. Only applications designed to take advantage of the right scaling API's will look crisp on both displays in that case. The other ones will look blurry on the non-primary display. MacOS does tend to handle that situation a little bit better.