hm, I don't use the downhaul without using the rotation. Pulling the downhaul only opens the leach and the lower part of the sail stays full. Thats good in waves and chop, but in most cases it is better to make the whole sail flat (=rotation plus downhaul) not just the top. But this might be different from boat to boat, sloop or uni, conventinal or wing mast.

Also I don't play the downhaul/rotator all the time (again depends if you are single or double handed). Better concentrate on course, sheet and pitch trim and only correct the big stuff with the sail trim. Maybe not the fastest way, but works for me.
Cheers,

Klaus