In 80% of cases, everything turns out to be exactly that toxic way, and either I have to heal the entire raid alone as a healer, losing a huge amount of mana. Or I have to think only about my own survival instead of wall-to-wall pulls and uptime playing as a tank or dps.
If your percentage is correct, I would suspect that you are potentially overhealing. This may not be true, it's just a gut first impression. I have played with a number who make me feel like a solo healer, and it's stressful, but I can't agree that the percentage is that high. I *tend* to be a responsible healer, but if I have a co-healer who on their own accord isn't doing much offensive output and tends to overheal, I do lighten up on the healing. There's no sense in overhealing the overheal. At the same time, I am also an aggressive WHM. I absolutely will DPS, and I will not play the game of keeping everyone at 100%, as overheal is a waste of MP, a waste of effort, and in end slows things down for everyone.

That playstyle isn't for everyone. Some people believe that healers shouldn't DPS, or do so at a very sparing pace. The way I see it...if the party doesn't die, and if I have a co-healer my effort healing lines up, there's really nothing to talk about.