When you look at them as a tool for arranging or creating samples some of what you say is pretty true. They're quite versatile, though, and taking it as far as comparing them to a cd player or even protools isn't quite so accurate. If you look at what turntablists such as Mix Master Mike (of Beastie Boys) do I think they can definitely be considered to be actual musical instruments to some degree.
He has solo albums, and if you search for his name on Youtube you should be able to find either videos of him on his own or with BB.