Because healing exclusively and ignoring 90% of your powers wasn't a good idea? Now i'm starting to think your the kind of player who refuses to learn how to improve at the game :/.
You had 18 powers in your primary and secondary. Lets say your empathy. Only 3 directly heal, one is a res, another regens health but not all that fast. So thats 5 powers of those 18. Now if you ignore fortitude, which could buff players defense ratings over 20%, well your letting them take more than double the damage they should be taking. Now, if you factor in how much damage a full 8x mob could inflict, you'd find them doing about 1,000 damage/second, when you factored in cooldowns in your own heals you only could likely heal between 200-400 health/second.
With no damage mitigation, people will die to that over time. But were not finished. The mobs love to "Alpha strike" and unleash that damage in far less time than over say 10 seconds. So you get the "Unlucky" burst people speak of, of 5000-10000 damage. Thats fatal and you'd have to res the person taking that kind of alpha. But with capped defenses your looking at only taking about 100 damage/second with an unlucky alpha of often being only 200-1000 damage at most, usually due to everything but one guy missing.
Lets also remember we have to be preventing debuff effects some attacks have. Some can cause a defense debuff which is very, very bad, for characters with high defense it can suck but it sucks even MORE for characters with no defense, those alpha strikes turn into 10000+ damage alphas even faster and easier. OR it's -recharge, in the early game you'd see this with the vahzilock or a slow effect. You want to be trying to prevent all of them from happening, defense was one means. You could also debuff the to-hit, or even do both, which an empathy/dark defender could do. Or heck, an empathy/energy blast defender could keep people off their feat and prevent attacks outright and thus, damage outright.
Which brings us to the attacks the attackless pure-healing "Healing is my full time job!" empath ignores. They have crowd control effects such as knocks, or
I was saying I wouldn't take a pure healer, because pure healers don't buff. They do not use fortitude on anyone 90% of the time and the lack of attacks also means enemies live longer. But not only that, enemies get to fight at full strength ignoring dedicated debuff powers, as all attack SETS have some secondary effect or another. A few are damage/extra accuracy but most are some kind of debuff effect that your not using. Because you are not using those debuffs, enemies are being allowed to be harder for the team than they need to be. Your giving the enemy some initiative and giving up initiative of your own.
I saw an empathy/dark blast defender with no attacks and didn't have fortitude. I was facepalming. Because I had a similar character with dark blast attacks and by attacking, my teammates took far, far less hits, and thus far far less damage. Especially as I always had fortitude on them as much as possible. I didn't heal much on her because I didn't have to, and I was doing damage to. It was not a full time job.
No, I am not being the stop having fun guy, I am being the experienced defender/corruptor/controller player who has played multiple different powersets to conclude that there was no perfect combination.
But I could conclude there were a small, small number of poor ways to play the game, and they all had one thing in common; they
ignored or outright skipped most of the powers they had in their primary/secondary every time. The attackless empath was as bad as the taunt-bot tanker for one similar reason; they forgot they had a secondary and didn't use it any even if they had time to because they skipped the powers. And often didn't even use their primary fully. And so the team payed for it, frequently and unnecessarily.
There is a reason in roleplaying, my empathy/dark defender called pure-healers sadistic masochists. Because the joke was, they allowed their teammates to take the full pain and damage, and heal them so they could be hurt all over again. It was a joke character made to deconstruct bad empaths and show how to really play empathy. Not the only way of playing, just not one of the really bad ways of playing her.
There is no right powerset just you don't want to be ignoring all your abilities like the full time healer does. If you have 45% defense on everyone in a team, only 10% of the damage will get through at most. If you add crowd control in there or resistances, the damage taken will be even lower to the point you don't have to touch the heals, so if you could only heal and had no other abilities then I hate to say this, you'd be bored to tears and I saw that happen quite a few times to attackless, buffless empaths :S.