Sword Oath is incredibly powerful. Paladins in 2.0 had very poor potency attacks in their combo which was what held back their OT damage. According to Xeno, one single target his Paladin co-tank is keeping up with his damage when either are OT. Sword Oath adds 50 potency to every hit--its a separate line in the combat log and scales like an ability.

Most swords are on a 2.0 delay, or 30 attacks per minute. From sword oath we have 1500 potency per minute (3x fel cleaves). FoF over its duration equates to roughly 10% damage (vs darksides 15%), and that leaves you with base potency attacks. Goring blade is superior to scourge, and royal authority while not better than dark side + soul eater, can be spammed unlike the former (which drops dramatically to 260 when not dark arted).

DRK still is better than paladin in damage--closer to War, but I don't think the differences are what you sighted, but more so the 2000+ off GCD potency a DRK has every minute or so between free clicks.