I was yesterday the first time in Shinryu Ex. The QTE there is extremely short, I finished it by mashing the square button on my controller only with 0.16 seconds left. When I started to roll my thumb around on the D-Pad and mashing the square button less hard at the same time I finished with over 3 seconds left.

So if you have a controller rolling the thumb around on the D-Pad instead of mashing buttons could help?