The problem with Windows is that you do not have the source code so you rely on excessively brittle hacks. For example when i was using Windows 8 i used to run some program that forced some handle that uxtheme used to close which caused controls to fall back to using the classic win9x theme (which was disabled on the UI in Win8) - and for that to work it had to freeze some system process for a bit, force the handle to close and unfreeze it. That process worked for Win8, it broke on Win8.1 until someone found a workaround but you had to replace some apps with alternatives to work and was completely broken on Win10 (and i guess Win11 too) and was never fixed.
Meanwhile if i desire i can download the official source code for Gtk and modify the painting code to be as pixel perfect as i want (and in fact i did exactly that some years ago to make XFCE look like Windows 95 because the available themes looked off :-P).
For webapps, yeah you can't do much but personally i prefer local apps where possible anyway - and for the other stuff, if i care enough, Stylus and Greasemonkey are there to help. I do use a custom Stylus theme i wrote for HN for example :-).
Meanwhile if i desire i can download the official source code for Gtk and modify the painting code to be as pixel perfect as i want (and in fact i did exactly that some years ago to make XFCE look like Windows 95 because the available themes looked off :-P).
For webapps, yeah you can't do much but personally i prefer local apps where possible anyway - and for the other stuff, if i care enough, Stylus and Greasemonkey are there to help. I do use a custom Stylus theme i wrote for HN for example :-).