I guess it depends on whether one wants to believe that Ueshiba M.'s techniques, and by extension Saito's techniques had no technical flaws/unsuitabilities to begin with. They were all human after all. Maybe Nishio saw something that he thought did not make any technical sense when applied to certain situations.
Aikido is constantly developing, I don't think anyone's technique stays the same as they evolve in training. As a result, a book can only capture a moment in time, based on the author's understanding at that point in his training.
Just my thoughts.