Hi - I have had a DF IV for several months and have similar concerns, but have learned to live/adjust for it somewhat.

After mild training crashes, I would notice that that drift would become suddenly excessive. What I learned is that one of the mounting points on the PCB was not attached perfectly to the leg- it would be just above or below the board or slightly pulled back - hard to spot when you are outside. A quick reattach always improved the drift. Also make sure the frame members are straight and not askew along with checking to see each motor is straight with a bubble level.

I agree 100% that watching the various DF videos, it does appear that other DFs have little to no drift, if you find out the cause from the manufacturer please let me/us know.

good luck and enjoy!