i am not a controller user myself but i tend to see ppl assigning high frequency skills to their go to buttons,especially the ones that wont conflict with left analog stick,plus its always good to add an additional hotbar just for monitoring all ur cooldowns

in the end i think it all amounts to how fast u r tapping and switching with ur controller,
hell,theres even a sch who managed to solo heal t9 with controller,and the way hes swtiching between skills and targets just looks insane