It *should* be just the task of keeping people up, hale and hearty, with the periodic tossing of spells to make the enemy the opposite.
But just as there has been power creep resulting from the constant increase of champion points, allowing people to pump their stats to the point of imbalance... so too there is a condition of skill creep from how many skill points there are, allowing people to spread beyond one role and fulfill two or even all three in lighter content. At least, under the current skill system structure, the skill points allow such skill creep.
I used to think that the loss of a need for a healer was due to the content, an overuse of one-shot damage attacks that are easily defeated by following the fight mechanics, that thus reduced the challenge to the players enough to make small-power heals into a viable tactic. I thought that was the reason that tank+3dps was a thing, how the dps can just dodge the big hits and pop a vigor to cover the scratches of the trash mobs.
More recently I've come to conclude that the ability to cherry-pick later skills is a contributing factor. Spending 2 points on a morphed orb, bypassing the 4 lower skills. Grabbing a morphed vigor without any investment into the lower ranked Assault skills. There's no ultimatum involved such as with choosing skills to go into the limited bar space that push players toward offense or defense. Coupled with the push to have any character be able to achieve minimum capability in any role or task, this is a problem that results in no clear role boundaries.