Peter - I think that is a strong possibility. Previous to the war, you had a loyal son, not an athlete or tough guy, and not naturally drawn to his father's world, either martial or spiritual. Confronted, so to speak, on a daily basis, by many men who were not only stronger than he was, but stronger than he ever would be. (A little digression - I'm not thinking of size - I think Shioda and he were about the same size - but we have talent, fighting spirit, all sorts of things that make the man).
But in Tokyo, Kisshomaru went to war, so to speak. And people who've actually been to war and survived do not need to feel that they have to hang their head in relationship to a ring fighter or "martial artist." I can imagine, at least, that when Kisshomaru was confronted by the arrogance of one or another of these sempai/shihan, he could hold the internal sense of, "I was dodging napalm. I kept this dojo in existence. I stay without any possibility of even fighting back. And furthermore, despite your exploits in war, you were part of a group, and one can always borrow courage from the group. But I was alone." Diplomat and politician he certainly was, but all the times I observed him, I never had the sense that he felt himself abashed in the slightest when dealing with his seniors, the off-shoots (Shioda, Tomiki, etc.) or the top shihan in his organization.
I hadn't thought of it this way before, but I've certainly wondered why Morihei "let him get away with his changes." He was still the boss-man. To be sure, there the idea you raise of the old men making speeches at the wedding, listened to assiduously and then ignored. But one gets the sense, in the interviews they did together, that Morihei gave his son his head, so to speak. As in, "whether I agree or not - and I may make some noise now and then - you are a man and make your own decisions."
If this is so, how admirable. I've seen all too many great martial artists in Japan and elsewhere with non-entities for sons, the latter never finding a place - or merely being a place-holder.