OP, I hope to GOD that you are trolling.
If you're serious, then you're embarassing us Dragoons. :(
Chaos thrust is important for outputting your maximum damage as it leaves a DOT effect. (Damage over time) when used correctly in its combo.
Please...learn your job. You remind me of this dragoon I had in aurum vale who just spammed heavy thrust and piercing talon while circling the mob.
And another dragoon that I know who didn't know what any of his abilities did until I scolded him to learn it.
EDIT: deeper into this thread it seems you've figured it out. So, here's your lesson. Never go into anything without knowing exactly what your abilities do. The biggest mistake I always see with fellow dragoons is they don't know. I will literally say "Why aren't you using heavy thrust" and the answer will be "I don't know what it does" or "it doesn't do anything."
