Are my mitigation numbers off ?

[Reynhart]

Average mitigation isn't everything. PLD uses cooldowns individually and gets the full benefit of them. WAR and DRK stack Inner Beast and Dark Mind with other cooldowns which means that they're less effective. Sentinel itself is 40%, Inner Beast+Vengeance is only 44%, not 50%.

Yes, but for each Rampart, WAR can use one Inner Beast.
And, unless you have two big hit closer than 15s, for each Sentinel, WAR can use Inner Beast+Vengeance.

Since Shield Oath already applies a 20% damage reduction, Sentinel is also not really -40% from "base" damage.