Possible Paladin Rework...

[Giantbane]

Don't forget the 20% to heals from Defiance when calculating eHP since that is where their eHP boost mainly comes from.

No, Alphras is exactly correct. eHP is just the number of hits you can take before you die without heals. What you're talking about is sustainability, or the amount of healing required to restore the tank to full. SHO is actually more effective in that regard, since the PLD is taking 20% less damage, he requires 20% less healing. Defiance provides 20% MORE healing, which at first glance seems the same as what SHO is doing, but it's not. In order to compare the two, we need to know how much LESS healing is required due to defiance. First you invert it to determine how much healing is required to heal to full with defiance on:

1 / 1.2 ~= 0.833333

so a WAR requires about 83% as much healing to be healed from 0 to full, which means they require 17% less healing due to Defiance, which is slightly worse than the 20% less healing needed when under shield oath. However, a WARs self heals will cover that discrepancy in most cases.

Rampart and Inner Beast. While IB has a shorter uptime, it can be used more frequently as long as you are doing your rotations which results in approximately the same overall uptime for the two. The differences: IB does damage and has a self heal, but the big one is that they actually don't mitigate the same amount because of ShO being a base % damage reduction which means Rampart actually ends up being a 16% damage reduction while IB is still 20%. Also, as far as the difficulty of timing IB to big attacks, Infuriate + IB is available more often than Rampart so while you have to push one more button you can time it to more potential big attacks.

Sentinel and Vengeance. Sentinel with the trait says it does 40% damage reduction which actually results in a 32% damage reduction and lasts for 10 seconds and is on a CD timer of 180s. Vengeance does 30% damage reduction, does damage on being hit by physical attacks, lasts for 15s and has a 120s CD timer. So they have almost the same % damage reduction, but Vengeance does damage, lasts longer and can be used more often.

You're looking at these two wrong. You have to remember that while the eHP of a WAR and PLD are the same from Defiance and Shield Oath, the WAR has more actual HP and the WAR is taking more damage, exactly 25% more damage to be exact. This has been left out of your comparisons. In truth, the 20% reduction on Rampart is exactly as effective as the 20% reduction of IB. There's no difference in how it works in practice.

For example.

You have a PLD with 8000 HP. War in the same gear would have 10000 HP with Defiance. In this instance the WAR can take 10,000 damage before dying. The PLD in shield oath can take the same 10,000 damage before he dies (10,000 damage x 80% damage from shield oath = 8000 actual damage done to the PLD in this case, just enough to kill him). With Inner Beast active, the WAR can take 12,500 damage before he dies (12,500 damage x 80% damage from inner beast = 10,000 actual damage done to the WAR). With Rampart active, the PLD can take the same exact 12,500 damage before he dies (12,500 damage x 64% damage from both shield oath and rampart = 8000 actual damage to the PLD).

As you can see, both abilities are working the same way and allow the tank to take the exact same amount of extra damage before dying.