I disagree. As soon as you add a dedicated support or debuff class, one of two things will happen. Either the class will be very effective, become Required (TM) and the game encounters will be designed around it, thus completely negating the intended purpose, or the class will have little impact on the end game content, and will no one will play them, outside of a few fans. Inevitably, raids will ask those players to switch to a more useful class. It make seem counter intuitive, but the trinity system gives designers more flexibility when designing new classes. The bard is a great example of how a support role works. They're capable of providing some useful (but not required buffs), but are competent damage dealers.