Not trying to be contentious, but the fact that he promoted others 10th dan sort of bolsters my argument, which is that, if Saito had a truer grasp of the art as O-sensei taught it, then why didn't O-sensei give him the recognition he extended to Tohei, Suenaka and others? And if rank and licenses really didn't matter to him, why did he bother granting them?
He handed out ranks for various reasons. In Suenaka's case I believe it's because he needed a teaching credential when he moved to Okinawa. There were other people who received ranks for similar reasons. One person was awarded a 9th dan - Ueshiba just asked him what rank he wanted and the person didn't feel comfortable asking for 10th.
There weren't any ranks at all until 1942 - they started because they were required by the consolidation of all Japanese martial arts by the Japanese government under the Dai-Nihon Butokukai.
First 8th Dan - Kenji Tomiki.
BTW, I'm not arguing that Saito had a better grasp (or a poorer grasp) of anything in particular - just that he was in a position to see where Ueshiba was - with him in Iwama.
As for his rank - maybe he forgot to ask for it