Hello Luckyclan. Why do not you make a version Artstudio for windows? You have a unique brush engine - which is not in more than one Windows program for painting. You would not have competitors.
The price of your program is very low, I would buy more. You lose profits without releasing your application on Windows.
See: most will never buy ipad 12.9 - it’s expensive + it’s also a separate keyboard + pen. It is small, you can’t work on it for a long time - eyes and back hurt. It is suitable for sketches. It does not compare with monitors. Many do not like the feeling when you drive with a pen on the glass.
Mac devices, too - many do not fundamentally buy. They are also expensive.