I wouldn't call the current state of our healers descent by any means. Functional? Sure. But in a good or even descent state I would have to strongly disagree. Healers aren't even really healers in this game. They are support DPS, and their offensive toolkit is totally braindead. Identity is a strong issue with AST and is currently making any kind of balance impossible; WHM has too many issues to even list here and would need its own thread. All the while SCH is sitting on a throne, legs crossed at the top of the hill saying, "Sup?"
This role has traversed so far beyond the original intent. The amount of ogcd heals is ridiculous, and if they were eliminated, reduced, or given much longer CDs healers would spend more time actually healing. Obviously, they need their offensive toolkits in order to do solo content, but to spend over 90% of their time DPSing in PvE and still call them healers is just crazy. When Yoshi talked about a restructure to healers, I have good feeling of what the man's intentions are.
A big reason why old content at min ilv is much more challenging is because the majority of ogcd heals are stripped away and/or they become much more reliant on hard casted restorative spells. Now having to heal 90% of the time isn't necessarily the answer either, but it needs to be MUCH higher than 10%. Getting to that 50/50 ratio between healing and DPSing would be a comfortable ratio for most healers I believe, and during that 50% that is DPSing they can most certainly make it more interesting than just spamming your filler spell.
You are correct that perfect balance is not really possible. It's a hanging carrot. But healers can most certainly be more balanced than they are currently. Because when WHM has no distinctive advantages over the other two healers things are not only unbalanced, they are unfair. Ramping up WHM DPS is not the answer. Making it easier is not the answer. Adding a 4th healer is most certainly not the answer. The only way to truly balance our healers is rebuilding them from the ground up. I totally agree with Yoshi and we cannot keep up the pure healer/barrier healer set up. Since he has pointed this out specifically, expect it to go away. I think they will still have strong and even more integrative DPS kits, but we will no longer have as much time to use them in group PvE.