A cursory look at WAR and PLD lead me to conclude they were designed within the idea of "main tank" and "off tank." The idea was that you bring a PLD as the person doing the bulk of the tanking, and the the WAR is there to tank when an additional tank is needed, but is primarily a DD.

The idea isn't that you CAN'T use a WAR as a MT, but that PLD, being wholly specialized in a tank role, should be the superior choice. My argument is rooted in Hybrid vs Specialized, because that is what each classes' design seems to point at: The hybrid WAR, the specialized PLD.

1) Reduce WAR damage:
Insofar as making a balanced class, this is the obvious route. Make them deal less damage to offset their ability to take hits. This allows them to still retain their versatility without outshining PLD in tanking.

2) Increase PLD enmity output/decrease WAR enmity output:
This requires prefacing: I believe that enmity control should be something a DD has to worry about. If going balls to the walls, willy nilly of enmity is required to clear content for a properly geared and competent party, that is poor design foremost.

If it remains that DD need to be capable of all cylinders firing DPS, then PLD needs to facilitate that completely by having more Enmity output, whereas a WAR tank should require more thought towards enmity control on behalf of the rest of the party.


3) Increase PLD survivability: This is actually pretty concurrent with the OP's suggestion. If a PLD took less damage or was able to mitigate that damage better(for example, say better self healing). Then this creates a situation where WAR, 5DD, 2WHM is mostly parallel to PLD 6DD WHM. Will WAR 5DD 2WHM get the job done? Certainly, but PLD 6DD WHM will have an easier time.

4) Increase PLD survivability and minor increase in enmity, decrease WAR enmity output:
This is my preferred answer, mostly because it brings the two classes down onto the same level. This also facilitates WAR 5DD 2WHM being roughly equal to PLD 6DD WHM.

How to achieve this balance has been brought up by many people, so I won't bother repeating it. However, I agree with several points brought up.

MP gaining ability, auto-refresh, or passive MP cost reduction.:
While I love the concept of resource management, it seems to me that MP is drained far too quickly. The MP pool tends to bottom out very quickly and cannot be regained nearly as quick or in amounts significant to do anything with.

Ideas:
Give Spirits Within a MP restore component(say 1/4th to 1/2 the damage dealt.)
Give Outmaneuver increased MP gain on block(I think any pld in their right mind would agree the current amount restored per block is laughable at best and useless at worst.)
(Stolen from WoW) Allow heals on the PLD to return a % of MP, either static or based on the amount healed. (Say, 2% of MAX mp every time the pld is healed, or 25% of the amount healed also restores MP)


Give Parry back to shield users, or vastly increase the mitigation provided by block.
Lets say parry completely negates damage. If something attacks 10 times for 10k total damage, and you parry twice, that means you've taken 2k less damage. Lets take the same numbers, except you shield block 4 attacks for 500 damage per blocked attack, you still take 2k less damage. Complete negation LOOKS better on paper, but so long as the end result is the effectively the same, it doesn't matter.
Likewise if you give parry back to PLD, you increase their survivability by increasing their means of mitigating damage.


Or just nerf WAR into the ground, then there's no choice BUT to pick a PLD.