I never said every character needs to be fully optimized. I'm not a min/max player. However, a dedicated healer is just not a needed thing and I think you're missing what we mean when we say "dedicated healer" as it applies to this game. A "dedicated healer" is someone like the OP--a person who usually picks empathy and picks pretty much only the powers from the empathy powerset, and often dips into the medicine pool for even more heals, and then contributes nothing else to a team because they're waiting for green bars to move.
Yes, even in a duo that's useless and wasting one half of the duo's time. Whereas if that same empath were to actually pick up some of their attacks and offensive powers, now they can fill time in between buffs/debuffs/healing with attacks. Sure, they may not do much damage, but the faster mobs are dying, the safer everyone is anyway. And yes, this applies to running in a duo as well; in fact, I would think it would be even more prevalent in a duo.
And for the other people trying to say that healing is necessary and yada yada--we know. We have never said that healing cannot be useful. I have a water/pain corr who once spent a good chunk of a TF healing instead of using her attacks because for whatever reason the team was quite squishy. Healing has its place, but it should never be the only thing you focus on. @Nemu summed things up quite nicely in their post and their description of how to play empathy is what I aspire to be on my pain defender; but that doesn't mean I don't also take my attacks and slot them.