My idea to make Phantom Dancer a duelist item

Currently the damage reduction passive is garbage. Even buffed to 16% it will still be garbage.

Instead I had an idea. After taking a certain percentage of max health in damage from an enemy champion, you gain a shield that only works versus that champion. It would work similar to hexdrinker, steraks, but rather than just working towards all damage, the shield would only affect the person who is most focusing you down. Alternatively, you could make the shield proc off whoever you last hit when you hit the damage threshhold.

Would this be unhealthy, weak, or overpowered? Not sure. Just an idea I had as phantom dancer is currently awful