Design of DRK and PLD

[Enkidoh]

PLD doesn't use it's shield? Uh, lets count the shield-based abilities PLD has:

Shield Bash is heavy physical attack plus Stun but has a slow speed (so you don't spam this)
Shield Lob that is a ranged attack for low damage but high hate (so is the main 'pulling' ability, again, it's not meant to be spammed)
Sheltron resulting in a guaranteed block with the shield for the next physical attack while the effect is active (for 6 seconds).
Passage of Arms throwing up your shield in front to magically defend your party behind you with glowing angel wings.

To say nothing of other abilities technically involving shield in principle or theme (like Cover, Sentinel, even the tank role ability Rampart was originally a GLA/PLD class ability).

And I'm probably forgetting some too but they're the big ones. We also had a few others but they were removed in past expansion launches (Shield Swipe, Shield Oath - this became Iron Will and was guttered of it's defense boost incidentally).

And what do you mean PLD is a 'regen tank'? It has no regen abilities at all - it has a single healing spell in Clemency which is a burst heal, I think you're confusing it with WAR and GNB which do have regenerating abilities. PLD is all about defense and SE's description for the Job on the Lodestone (along with it's GLA base) all but screams "this is a defender".

I'm sorry, but I simply have no idea what point you are trying to make here.