Are my mitigation numbers off ?

[Reynhart]

I think to get a full sense for it, you'd also need to calculate in effective block rate/amount and effective parry rate when geared in BiS gear.

Isn't Parry useless when Block procs ? Meaning that DRK and WAR also gain more than PLD from stacking Parry.

Yes, my calculation assumes 100% usage. With shorter and more frequent mitigation, I think it'd only widen the gap in favor of WAR.
Also, I feel I've been a little generous with PLD or DRK, where as WAR's mitigation seems pretty accurate.
As for cross-class skill, the only real mitigation skill is Foresight, which is also better on WAR.