PLD theorycraft?

[Donjo]

I crunched the numbers and found that stacking Parry is more useful for Paladin than it is for Warrior. This tiddle is for a Pally using a 110 or 115 Kite Shield. If your:

Parry is around 600(~30% parry rate total)
110/115 Shield(~30% block rate)

Here, your chance of mitigating a physical attack is a function of the probability of either one of these things independently occurring(with the small caveat that both cannot occur at once and Block is checked before Parry as far as we know). When they're both about equal, it peaks at about a 41-42% chance of one of them proccing. That is significantly higher than a Warrior can reach even in a max Parry build. I personally consider 50% as the threshold at which Parry rate will actually matter in terms of how often it procs, and that's actually pleasantly close.

[Rbstr]

I crunched the numbers and found that stacking Parry is more useful for Paladin than it is for Warrior.

This makes no sense given that blocking happens before parrying. That reduces the value of a parry point considerably. (you've also done your math incorrectly unless you're using numbers other than the ones you posted).
If you have a 30% block rate and a 30% parry rate you're going to parry about 18% of the time (that is 30% of the unblocked 60%) for a total of a 48% chance to do some mitigation.

But 30% parry on a warrior means you're going to parry 30% of the time. So a point of parry on warrior is 1.7ish times as much mitigation as it is on a paladin with 30% block rate. Obviously this number changes with block rate, it it would always remain that parry does more for a warrior than a paladin.