Kishi made it so that Juubi jinchurikiis can't phase through dimensions. So that's one OP ability down. Madara demonstrated that JJ can travel but not phase parts of their body.
This means he could use Kamui onto others.
Kakashi took some chakra without the Kyuubi cloak that Naruto gave him with just taping his hand and said his Kamui became 3 times more effective to the point he could put Hachibi into Kamuiland.
Imagine Obito using the full power of 7 beasts with Kamui to wipe the alliance.
Discuss what do you think , don't forget I'm talking about JJ Obito