Don't take it personal, but I'm going to ask you to support some things.
<clutches pearls> Oh, the horror!
I'm not competent to claim that this or that Aikido technique isn't
in Daito-Ryu, and I'm not going to try. Instead, I focus on what O-Sensei chose to demonstrate vs. what Daito-Ryu masters choose to demonstrate. Public demonstrations may not be a perfect representation of the art, but they do at least show what the master in question thought people should see of their art.
So have a look at the 1935 Asahi news file video. That's fairly early on in the Daito-Ryu/Aikido transition, but there's nothing there technically that would look out of place in a Modern Aikido (tm) dojo. Well, except the general excellence. (And the weird habit of ending with one hand high, palm up, the other low, palm down. What's that about?
Conversely, there's not much there that looks like what Daito-Ryu people choose to show when asked to demonstrate their art. Perhaps there's little there that they couldn't show if they chose to, but they don't generally choose to--it's apparently not what they consider most important.
So it seems to me that at this point O-Sensei is already demonstrably moving in a new direction. Couple that with the story of him escaping Takeda Sokaku by sneaking away at night, abandoning his (Daito-Ryu) dojo to his former teacher, and the story writes itself.
Sagawa and Kodo, as you point out, continued to call what they did Daito-Ryu. Why, when O-Sensei did not? Could it be that though they saw themselves as modifying the teaching they received, they saw their own arts as extensions of Sokaku's art? Whereas Ueshiba saw what he was doing as something essentially different?
And again, the reaction of the other martial artists of his time. Did they go to Sagawa or Kodo, asking them what they called their art and refusing to take "Daito-Ryu" as an answer? Yet it seemed to be accepted that this Ueshiba thing needed a new name.
I don't want to downplay your point that O-Sensei infused his art with his spiritual insight, by the way. I think that was certainly a key influence on what he decided to keep and what he threw away. In my view, he kept the movement that reinforced the spiritual attitude he wanted to engender: centered in the six directions, neither aggressive nor defensive, overcoming conflict by negating conflict. That became the core of his art, and he threw away extraneous techniques like a sculptor throws away all the material that doesn't contribute to the image he wants to present.