He wasn't fighting Sas seriously
he used perfect Susanoo to draw out Oro and teach him how to use the mangekyo on the fly through battle. Just like Kikashi and Kabuto, Itachi wasn't fighting to kill if he were they would have been dead. I think we are reading way to much into a statement Itachi made to keep his cover and avoid unnecessary fight with an allie. Itachi basically was on par or a better tactician than Shika and Kakashi, master in many jutsus, given praise by the goat 1st Hokage, Danzou, the 3rd, Obito, Kisame, etc, the ultimate cheat code with that sword and perfect Susanoo, mangekyo, etc........... he's a top 5 shinobi. Naruto, Nagato, and the 4th all surpassed J-Man he's the goat teacher.