its to do with the need to energise acceleration and momentum against inertia during the turn downwind, and then turning the excess speed back into height during the turn into wind.
In defining Inertia, and talking about speed, you are reffering to velocity in which frame of reference?
BTW, I have landed a Ram Air Parachute over 1000times and flown conventional Gligers extensivley. Does that count as a big enough appeal to authority?
As to my experience in holding in high winds, we are talking about holding at 240kts odd in 100kts of wind. If turning downwind had any appreciable effect I would have noticed.
Please outline how you think the fact that the air is moving in relation to the ground effects an aircraft that isn't TOUCHING the ground.