Not any more of a stretch than pretending Dragon Roar or warrior shout abilities somehow preclude a bard class.
I would actually say that's one of the stronger arguments for Bard, not against it. It doesn't need a themed expansion to be introduced, because it is such a fantasy staple, and because there are plenty of minor traces of sound magic and several bard NPCs. It would be very natural for characters to pursue this rich and abundant source of power that isn't currently being taken advantage of by most people.
Much like how races in Cataclysm looked for new avenues of power in the form of new class options.