My experience one month into FF14 , some questions.

[StriderShinryu]

Most people have already covered the healing question but one extra thing worth nothing about that is fights, particularly boss fights, in FF14 are very scripted. If a healer knows the rotation/flow of a fight and what/when the incoming damage is they can often cheat on healing quite a bit. For instance, if they know it's going to be 30 seconds before the next attack that hits something other than the tank, they may choose to not heal the DPS until they have to (or until their heal spell of choice is off cooldown, which they can also plan around the rotation of the fight). Same thing for the tank. If they know that there won't be major tank damage until the next tank buster in 45 seconds, they may opt to not heal them yet and just trust the tank to mitigate with cooldowns (as any good tank should).

Of course, that's not saying there aren't healers who prioritize DPSing over healing who have a very selfish approach to playing the job, but not always keeping everyone topped up in FF14 can actually be the sign of a good, knowledgeable, trusting healer rather than a DPS hog.