Board Thread:Theories and Speculation/@comment-36512555-20200202084241/@comment-9782468-20200203145902

Perfect Jinjuuriki are essentially protected against Genjutsu because their Tailed Beast can break them out immediately, thus negating Genjutsu's advantages.

They're not protected against Tsukuyomi though because Tsukuyomi unloads its damage too fast for a Tailed Beast to break out its host in time.

@Frwt, to clarify your question about Jiraiya talking about Genjutsu. I believe he said in order to break Genjutsu, you have to realize you're in Genjutsu, and disrupt your chakra to the point where it breaks the castor's grip on you. The latter half of that is skill dependent; for example, Naruto couldn't break out of Itachi's Genjutsu at the level he was at in the beginning of Part 2.