There were no "Healers" as recognized now; rather, Casters had healing tools atop an otherwise more variably purposable kit. CNJ was a 6-element elementalist who simply had some healing atop that, while THM was an Oracle who used Blood, Poison, Astral, and Umbral Magic and was as much a debuffer/nuker as healer / HP-transferrer.
The Physical Melee were referred to not as Melee DPS so much as "Fighters". Lancer, Pugilist, and Archer acted in a sort of triangle of capacities. Lancer acted as a strike-leader capable of granting TP (allowing allies to more rapidly ramp up to finishers) or Leech (healing on physical hit) to allies and longer-term sabotage via draining enemy TP (which slowed the frequency of their special attacks) and longer duration snares, and had passive eHP near to that of a tank; Pugilist had technically greater sustain via stance and CDs, though at opportunity cost to damage, and had greater immediate sabotage capacities via stuns, silencing, and pacification, and also had one of only two taunts in the game for quickly weaving in as a snap-tank; Archer had the largest range of kiting tools --snares, binds, a near-taunt, and a enmity purge tied into their invuln via Decoy-- and debuff purges, and because Mind and Piety both gave it decent overall value even for damage output, it tended to take on a spot-support role via discrete tools, rather than via embedded tools like Lancer or by changing stance like Pugilist.
Gladiator was your trick/counter tank and Maurauder your zug-zug tank. Every class could use the actions of others, though synergy obviously varied. Marauder, getting little benefit from Mind or Piety and having zero magic of its own, usually carried the least support, with Thaumaturge typically having the most healing throughput in practice and every class having its own variety of supportive tools.