The drag is from the constant mesh gearing, at least, it was on mine before I sent it back to Robinson to get rebuilt. Once it came back, with proper clearances, it spun incredibly smooth, functions better than any R3 I've ever felt, easy shift, butter smooth, exactly as they should be.
If it's dragging with the output shaft removed and just spinning the input in the bearing, it's probably just oil drag.
I firmly believe the massive clearances the gears have, to make assembly easy and cheap for Triumph, is to blame for the vibration some people have and some don't. Even with all the engine work, my bike is smooth in regard to vibrations all the way to 8000 RPM.