So I'll again turn the questions around to you, "What is Aikido?" Would you say that Nishio, Yamaguchi and Saito are all doing Aikido, and if so, what is the common thread that makes aikido unique and distinct from other martial practices?
I would say that Aikido is the quest to meet the goals defined in "Take Musu Aiki" by Morihei Ueshiba. Yamaguchi, Nishio and Saito all worked towards those goals in their own ways - and I have never seen those goals stated in that way as the primary focus of any other martial art.
That it hasn't solved all of the worlds problems doesn't make the ideal any less valuable, any more than violence in India negates Ghandi, or racial violence negates Martin Luthar King.