Board Thread:Naruto Discussions/@comment-27550669-20190130125246/@comment-31715856-20190204041047

When people say they're immune, they mean they can break the Genjutsu instantly. Remember, Bee broke out so fast the moment Sasuke turned his chest was blown apart. Also, the fourth databook does say that his status as a perfect Jinchuriki renders powerful Genjutsu ineffective against him.

Obito did not control Kurama when it was inside Kushina. Once it was outside, Obito cast the Genjutsu on it with his MS to control it. I'm sure it's possible to do something given enough time, but it's unnecessary. Remember, Naruto is the only known Jinchuriki whose seal was made to naturally feed minute bits of his demon's chakra into his system over time. Other Jinchuriki have to tap into it, the beast cannot just force the chakra in at whim. So I think controlling Yagura would have been enough, the Sanbi was less a factor.