Even within the Aikikai there were teachers that continued with the "prewar" flavor you speak of: Rinjiro Shirata, Bansen Tanaka, Morihiro Saito, Sadateru Arikawa etc. Even if Arikawa and Saito began training in aikido after the war, they had a harder, more combative style that you would never mistake for Kisshomaru's kind of aikido. And if you've ever seen a demo by Hiroshi Isoyama, then you'd know that there is nothing "pacifist" about it.
As Stan Pranin points out, Saito liked to point out the similarity between his waza and the waza of Osensei in the 1938 manual Budo as proof that he faithfully preserved the teachings of the founder. So the prewar/postwar dichotomy is too simplistic.
Thank you for pointing out Hiroshi Isoyama. Really dynamic, an inspiration to continue the methodology of Aikido as BUDO.
I found this very interesting article on Aikidojournal about Hiroshi Isoyama. This is a direct quote from the article, an interview.
"Some people were in contact with O-Sensei when he was spreading aikido purely as a budo; others only began learning from him once his thinking had evolved to emphasize aikido as "a way of harmony"; still others learned from him at various periods later in his life. All of these will have different viewpoints and interpretations, and I don't think it's possible to say that any of these is better than the others."
It's nice to know that one of the first generation students, persevered the the combative nature of Aikido.