I think machinist and Dark Knight are the only ones I can think of with a straight A->B->C combo, I haven't even maxed them out yet. Doing something like this would imply that you are supposed to keep those going all the time which is not the case. Everything has actions you need to weave in and there are time to ignore that combo for a time.
The "3 button combo" was chance based. I'm not sure if it was based on crit or just random, but the next ability in the series was not always available immediately after previous. Also you could have one of 2 turrets (one for single target and one for AoE) that were placed manually. May not have been more buttons, but clearly required more attention.
Everyone lost role actions.