This power would probably be kind of useless in a session with a healing class, but could a rogue maybe rage sine it deals with negative emotion, steal pain away from a wounded teammate?

I mean, Pain seems more a Doom Thing, not sure how broad Rage is in terms of emotions. Also is. Pain an Emotion? 

Either way, someone who takes the Pain away would work not as a Healer, but as an Adrenaline Rush. Healers can Heal a wound, but if you take the Pain away, you can keep going while wounded. Healing takes time off the battle, if there’s no Pain, there’s no Limits of how far you’ll push your body, you will just keep going until you can physically not move anymore. Not useless even with healing.