Yeah I think WoW had something similar in the concept of the Shield Spike (though this was fairly low damage). It would certainly be better as an automated attack rather than a button press.

Heck if Sword Oath can attack 50 potency attacks to your autos, why can't shield oath do the same but on block/parry.

THe current Reprisal/Shield Swipe mechanics dont do enough to warrant the factoring of increased mitigation but this is more due to the hugely lower returns on +% you get per parry point, and the meh potency of swipe. Definitely cleaning up their implementations could go a long way to making defensive stats viable.