The Dragon punch motion has also givin me problems. I’m playing on an madcatz te stick, but the only thing that will make a difference is practicing it over and over. A few tips some people gave me were… go forward, let the stick reset then quickly do the motion for a fireball, or berserker barrage. (Quarter circle forward) Another hint that helped me a lot was to think of the motion as doing a ‘C’ with the stick.
Don’t try to find shortcuts, or practice shortcuts, because when new games come out they most likely won’t implement said shortcut. Once you get the hang of it the DP motion is just like doing a quarter circle, half circle or any other ‘basic’ motion.