How about no. To make support classes work you have to gut the output on the rest of the classes to make the new support role necessary. Then you risk the further support of class stacking to multiply the out from said support class. Or you make the them unnecessary and everyone ignore's them. The former can create the "Princess <Class>" attitude and the later just disenfranchises players with a fondness for a class but unable to play due to being pidgeon-holed into unnecessary support.

To reference the Saboteur and Synergist comments. You are not meant to keep a person in that role the entire fight, but rather to swap them in and out of it as the fight wears on.