A couple of years ago I was in a similar predicament.
Not having the space for a desktop I initially bought a Windows Surface Book, big mistake, it didn't have the power I needed and wasn't upgradable, I sufferered it for just 3 months before I started looking elsewhere.
After a lot of research I settled on a Dell XPS 9550 and haven't looked back! The build quality is second to none, the screen is stunning and has more power than I'll ever need. I'm running all the Adobe suite - Lightroom, Photoshop, Premiere Pro, After Effects etc.
The 9560 is the most recent incarnation with the 9570 due out shortly, both fall into your price range.
As far as Windows is concerned, I've had zero compatibility or virus issues and all I use is Window's inbuilt Defender software.
Has to be added to your list of possibilities.