So...Why was Shield Oath level 40?

[Ultimatecalibur]

I believe that SE figured by math with equally geared tanks and dps that the 1.5x/1.6x Enmity stance was not needed until level 40. The problems that Paladins have in Hakku, Brayflox, Qarn and Cutter's Cry happen usually from level and gear disparity.

The only reason Warrior gets its 1.5x Enimity stance at 30 because the jobs mechanics are all built off of the Wrath buff granted by the stance.

Sword Oath Increases the potency of auto-attacks by 50. I mean, what the hell?

It doesn't increase auto attack potency by 50, it makes an additional 50 potency attack every time the Paladin auto attacks. Subtle difference that makes the Dreadwyrm Blade (auto attack delay 2.08 auto attack damage 40.21) slightly better than the Excalibur Zeta (Delay 2.32 Damage 44.85) in Sword Oath even though they have the same average auto attack damage (19.33).