Well, the ability in question also boosts defense to 115%, but for the parameters of how the skills work in my game, I wouldn't be terribly bothered to still have it removed.
Basically, I'm designing a boss who occasionally uses an ability called Bulwark that boosts his defense and regens 3% HP for 3 turns. One of the actors has an ability called Deadly Wound that they can only use when transformed, which is probably about 25-30% of the time - and even then, they typically only get to use a couple attacks before reverting back to normal form. So using Deadly Wound is a pretty big commitment of turns and resources (especially since other abilities could do more damage or apply other states).
I was hoping that the player could either simply do enough damage to chew through Bulwark, causing the battle to simply last a little bit longer, or they could use Deadly Wound to stop its healing effect.
Now, because Deadly Wound is, in short, a sort of "finisher" in a "combo point" system (that's not how it works, but it's the easiest way to think of it), I wouldn't exactly be against giving it the ability to remove Bulwark entirely. But I'd like the player to be able to proactively apply Deadly Wound and prevent Bulwark from healing later, too - that is, if Deadly Wound were applied, and THEN the boss used Bulwark, it wouldn't heal him until Deadly Wound fell off. It also would still allow the 115% defense boost from Bulwark to still function, as well.