...many people reported that the game really seems to stress the GPU on a constant level (more than 80-90% load all the time).
games I have run the GPU at 100% load. If anything, I would see less as a concern as it would suggest the game engine/graphics driver not making full use of the card(s).
...I mean the game stresses my GPU and my CPU (and obviously not only mine) more than let's say Assassin's Creed Black Flag which is quite impressive on high-ultra settings...
You are comparing D:OS with a game that's been out for 6 months (on Windows) and was produced by a studio large enough to commandeer limousines from Nvidia and ATI.
Give Larian 6 months with D:OS and you'd be able to draw a fairer comparison.
My only real personal complaint is that there are some framedrops from time to time and stuttering while scrolling the map.
That's probably not CPU or GPU-related then but an HDD (or SSD) issue. Try checking Event Viewer for any disk or IO errors and confirm (with the appropriate benchmarks and utilities) that your storage is as well set up as it could be.
