saying tongue weight goes down with WDH is like saying I just lost 20 lbs because when I was on the scale and pushed down on the counter the scale dropped by 20 lbs. No your weight stayed the same, you just applied an opposing force in another place and the counter to that force lifted force off the scale. It didn't change your weight at all.
That's all WD bars do. They apply an opposing upward force reducing the load on the rear axle and since the sum of the forces must equal 0 the counter to that force is downward force on the TV and trailer axles