Even the WAR's stance-dance comes with penalties. Swapping to Defiance doesn't provide an eHP increase until you're healed. Swapping out of Defiance when you were topped off is practically taking 20% HP of damage. But yes, the current meta makes those generally inconsequential compared to a lost GCD, or worse, lost combo-finishers (though in that case you should just be dropping Shield, finishing combo, and then popping Sword). Letting Oaths retain combos would in no way overpower (our current, underpowered) PLDs, nor would making them oGCD while retaining combo-drops.