Shadows cost a straight 80CE loss which is nothing like taking damage... At 1300 HP (nice average accounting for all races) that's the same as 57 damage. This is why PLD/NIN is so popular and has been for a long time. I would love to see proof of the contrary, so a link to that "All about enmity thread" would be great.
Also while a counter generates 0 hate, it also loses 0 hate and does more damage to the monster.
I feel the biggest problem with PLD is a lack of understanding how hate works...
I would love to see proof of you taking 0 dmg outside of Sentinel being fresh on anything above Even Match. A parse would be awesome, or even a picture of your chat log showing you taking 0 damage without Sentinel up. Maybe you have Ochain/Aegis but lets be realisitic a PLD shouldn't NEED those to be a "proper" PLD.
Also you should really run tests on how much damage you take with that "weak 450 def" against any NM in Abyssea and then test again with your 850~909 def you'd be sad when you realize that 400+ def doesn't do a whole lot. After all if def was really all that BLU would take the least amount of damage regardless of sub. Then when you realize that MNK with 100 def (if that) with Counterstance up is not only taking around the same amount of damage (usually less since a counter = 0 damage taken) as you but is also dealing more damage from the increased counter rate you'll realize why PLD tank sucks on easy mobs. For other DD jobs being better than PLD on easy to tank mobs look at the damage dealt difference, a WAR/SAM won't take less damage per hit than a PLD but they will kill the monster a hell of a lot faster which means less damage taken over the fight and a decent WHM will be able to keep either one alive which is why WAR/SAM would be a "better" tank, not only will they keep hate and stay alive but they'll kill stuff faster.
PLD sucks on easy to tank monsters, get monsters that aren't gimped by super buffs (hi atma/cruor) are higher level (hi Voidwatch, for now at least) and you have an area where PLD will excel in, other than that face it while PLD is a functional tank on weak monsters it isn't optimal.