How hard is it to sharpen D2 blade steel?

Very easy. Acute angle and light hand to finish. Sand paper also leaves a serrated edge for wicked cutting. Its more aggressive and quicker to sharpen as well and not difficult to master. At 5000 grit, you'd have to be an idiot not able to get to shaving sharp with it. 1000 and such like it is like a serrated steak knife edge. So that's another cheat. It won't shave but it will cut fast, though will also wear quicker as it's edge is serrated and not supported by a more uniform supporting edge. In simple terms the bits sticking out get worn off.