As a healer, I'm not disappointed at all. In fact I was relieved that there were no tanks or healers, partially because I want to play samurai and don't like tanking, but mainly because I don't think we need more tanks and healers. I feel like the more types of tank and healer you add, the harder the game is going to be to balance. For instance, if you make a healer that deals damage to heal, then that healer is likely to either become the de facto best healer (because it does more DPS than the others while still healing adequately) or useless (because it doesn't have enough healing to keep up with existing content). DPS, on the other hand, seem much easier to balance. As long as they deal approximately the same amount of damage, the game will still work.

The problem this game has with adding new classes is that so much content already exists. For example, if they did add a support role and go to a five-person party, they'd have to redesign literally every single boss in the entire game for the different party makeup. (Well, that or start support jobs at a high level and not let them do low-level content at all, I suppose). Every tank and healer added has to be able to slot in to every existing fight, which limits how different they can be from one another. To me, three of each seems like enough.