OAT weapons are beasts for Burn, however on HNM's or other difficult enemies where the Damage rating of the weapon can have a large factor in Damage-MobTP gain, the OAT's suffer quite profoundly. It depends totally on the target however. It's a reason I chose to Pursue the Severance(fire) instead of Ultimatum better to have both than yell loud enough to try and cancel out the other one's merits, but I wasn't in the mood to camp the NM's through the Ultimatum/Vengeance path twice.
Also, if you can obtain a high Double attack rating (Such as through corsair) then the Vengeance becomes somewhat of a moot point, but those instances are few and far between.