But they weren't sharingan genjutsus. They were the genjutsus that he activates when you look at basically any part of his body.D and Oro would beat Itachi in this condition. On both occasions both opponents were not expecting to be put in genjutsu and neither were out for a full out brawl. His Sharingan was still active, thus this had some affect whether it was his reaction time or something (may be wrong about this part).
That is why Itachi is so deadly, if you go back and reread his fights he starts literally every single one of them with genjutsu. It doesn't get a chance to turn into an all out brawl.
Like in the Sasuke fight, few people realize this but Sasuke didn't see through all of Itachi's genjutsus, there were multiple genjutsus and Sasuke stabbed two of the genjutsu Itachis and the second one just pointed back at the real one and Itachi was like "Whatever you still don't have the same eyes, you is going to lose"
So all that time that Zetsu was wondering what they were doing, Itachi could have gotten up and killed Sasuke, but he didn't (obviously because he wanted to seal Oro and let Sasuke "win")
Same with Oro, Itachi let him know it was a genjutsu, and then he cut off his hand.
And Deidara, it wouldn't have mattered if they were in an all out brawl or not, had Itachi made Deidara think that he is Itachi and that Itachi is Deidara, then he would have used his bombs on himself, it wouldn't have mattered at what point.
I think people don't understand just how powerful Itachi's genjutsu is. The only person to break it on their own was Bee and that is because he had Samehada and the eight-tails. Reread Itachi's fights and you will see how useful it is, he can win without moving. Now consider if he threw a genjutsu in while they were in the middle of fighting, he could make them kill themselves or a teammate. Easy peasy .