That is not a valid counter-argument. Graham did not state that Ueshiba Morihei originated a new purpose to martial arts training. He claims that O Sensei at that time gave a new purpose to his path and made it into a spiritual path. And that he expressed this by saying to Hikitsuchi "Budo is love".
The fact that the idea of enlightenment and peace as the ultimate goal of martial arts is very old and can be found throughout history in many different cultures and countries is here irrelevant.
I disagree, the idea that Morihei Ueshiba originated a new purpose to martial arts training is, in fact, the most common view in conventional Aikido. That makes it a reasonable interpretation when it's restated without qualification.