I would say that O'sensei had not completed developing Aikido at the time of the 'Hell Dojo', but you have a good point. Shioda was pretty much as good as it gets physically/technically (if a little rough with his ukes!!!). Even then though, I have met a VERY high ranked karate sensei who saw O'sensei around this period and he said that he was so pliable and flexible in his technique it was fantastic.
I think you have some good points though Yann, maybe I am very focused on what I believe to be the best type of aikido. As you say, your own Aikido.
I wonder if there is someone who has trained extensively in all 4 styles? I know Chiba Sensei went to the Hombu's of 3 of those styles.