Board Thread:Naruto Discussions/@comment-24514198-20140604211103/@comment-3568954-20140611125731

Obito specifically said that the Rinnegan is far to powerful. he said i also wasn't able to transplant the rinnegan into both eyes Even just this one left eye... i had lost to its overwhelming chakra and ability

and though i am not its original owner i have survived and made it all this way with just one eye

what he was saying is that the Rinnegan is overwhelmingly powerful. he survived by only transplanting one Rinnegan. before he had the shinju in him he was capable of using Kamui but after he was not shown using it so its safe to assume that it used to much chakra to control the shinju either that or he did not fill like he needed to use kamui because he was all but immortal