Why is shield swipe so bad?

[Gilthas]

Let's say you do 10 global cooldowns in a short fight.

Method 1:
150, 200, 260, 150, 200, 260, 150, 200, 260, 150. Total Potency of GCD abilities you did: 1980

Method 2:
150, 200, 210 (shield swipe), 260, 150, 200, 260, 150, 200, 260: 2040


In a short 10 GCD fight, you gain 3% DPS by using Shield Swipe, and this is only your GCD DPS. It will result in LESS DPS gain after you add Spirits within and Circle in the totals. If the fight only lasted 9 GCD, you would actually LOSE DPS from using Shield Swipe because you spent a GCD on shield swipe instead of building to Rage of Halone faster. This is what I meant by interrupting. I understand that it doesn't STOP the combo; I never said that it does.

The ability is awful. It is not even close to "your best DPS ability."

This is such a flawed argument. So how much DPS does an ability need to add for it to stop being awful?