Given that it only empowers your next direct damage instance, it can easily be consumed by accidentally light attack weaving, or dealing less damage with an ability if said added damage doesn't equate to the added damage of a light attack.
At the same time it's disproportionately effective on high-damage single-target abilities such as Merciless Resolve, while being near useless on a multi-hit ability like Bound Armaments/Flurry/etc. as it only empowers the first tick of damage, and not the whole ability itself.
Maybe could make it apply to all damage of a single-target non-ultimate ability? But can't say I'm much of a duelist, just looking into it atm.