I have read people make statements like "Shinto is the spiritual basis for Aikido…." and I think it's more important to understand that, in my opinion, Shinto just happens to be the form that O Sensei resonated with and expressed his spiritual connection through. One could say that Aikido, in-and-of-itself, is also a form that he expressed it through. The spiritual basis of Aikido, to me, is the experience(s) he had that revealed, what to him was, the "true nature of things."
My understanding is that "Shinto" is a term that denotes the essential/true nature of things, and that the dogma isn't the point so much as the vehicle used to arrive at the point, which is a deeper understanding of the interconnected nature of things. So from that standpoint, while I think it's perfectly accurate to say Shinto is the spiritual basis for Aikido, I agree with the point you're making.