I understand what you are trying to say, and I know the difference.
It's having one person more specialized to have heals when need be so the other players don't have to hit that heal button and can dps more or control the boss more - if there were mana issues or resource issues, I'd agree with you - but as it stands, abilities are only tied to cooldowns - meaning you can hit that heal button and go back to what you were doing.
I'll illustrate how hard it is for someone to try to be a dedicated person to help heal.
This is the best "healer" spec I could come up with at the moment:
the problem with most of the skills you want to use to help back people up is that they are 40 second cooldowns and above. In the span of near a minute people would have to avoid stuff and not die. Even then, the Guardian only has one actual heal he can control - the others all add "regeneration" or a "healing area" to a certain spot.
I tried to balance it more towards doing damage as well, as the main function would be to use staff skills in combat, then switch to mace/shield for support. The build is more about giving allies a chance to breathe in combat when necessary.
The best part about the build is that it's entirely unnecessary in a group - you can pummel through it with skilled players and not have to worry about heals but your own (and theirs!) but also take the higher risk of not have support skills. And of course, utility skills can be hotswapped out of combat (as weapons can as well) to better facilitate more support oriented approaches.
I will concede that it is possible to have a support-minded player in the group. Is it necessary? Depends on the content and skill level of the other people you play with.