the dragoon is penalized

[Shurrikhan]

Making Chaos Thrust last 30s would mean you would clip it every time you tried using it.

I can agree with most of the rest of this, but... having a longer DoT time is objectively better than having a shorter time, especially when it's being clipped and is therefore not balanced around in "on paper" calculations. It allows for greater downtime mitigation/flexibility and cleave potential.