Wrong op is WRONG.. going from 20% DR to 36% DR does not make you bad.
Maybe you don't premade often, or for that matter even win often, but if my healer is about to go down and I need to keep him up guess what I'm gonna do? Switch to Dark Charge--> Guard+Taunt.
Another example: ally dies, passes the ball to me, I'm near the goal line.. 20% DR vs 36% DR? Hmmm
Contrary to what you may think... a good assassin will most definitely stance dance depending on the situation.