Stun can be OP...i fully agree. Stagger and tm reduction can do the same thing...lock your opponent out from playing. Expose and tm gain can do the same thing as well.
As was mentioned before....it's all about speed and abilities.
Best way to stop any of that atm is by using Raid Han. U will still lose on D frequently but u can stop the chain b4 it starts on O by using him and choosing wisely.
Also, Thrawn has a fast base speed. Fracture is the 2nd best option and running the 2 of them together nearly guarantees u won't deal w/ chain stun-lock.