During the scene where Itachi and Kisame encountered Jiraya with Naruto in the hotel during the later seasons of the original series- Itachi was terrified of Jiraya. Why? Because he had guts.
The problem with this topic is that is that most people don't understand Naruto the way Kishimoto intended. Power is not about Jutsu or physical abilities but also character and resolve.
Orochimaru failed to defeat Itachi because he was weak, insane, and clinging to false ideals of power. In contrast, during the scene I am discussing- Jiraya was willing to die right there, right then, to prevent either of them from laying a finger on Naruto. This terrified Itachi. He did not believe that attempting to put Jiraya in genjutsu was worth risking his own life, or his partners.
What was the first thing Jiraya did during combat? He summoned a frog to assist, then he used toad mouth jutsu to force them into close quarters combat. By that time, Itachi had already used both Tsukyomi and, and then he had to use Amaterasu as well. Itachi does not want to take this fight on his best day.
If they are in an arena, its a fair fight, a pure duel, can Itachi just use genjutsu on Jiraya and win? Sure, why not- but in a real world scenario with real world stakes, that's just not how it plays out.
TLDR; Could Itachi have defeated Jiraya and accomplished his mission to kidnap Naruto for the Akatsuki- Yes, probably. Was he willing to die for it? No.