I don't see how blinding the juubi will give them an advantage. Kurama said the juubi's chakra is like senjutsu. The same type that Naruto has in SM. So he can easily sense where they are even if he is blind. But if Madara and Obito are controlling him, it would give them an advantage.
EDIT: they are not trying to kill him by attacking his eye( lol.. You really think like a kid don't you?). They are trying to handicap him. If your opponent is way stronger than you, you have to atleast handicap him to get an advantage. Also, we don't know if Naruto “CAN'T” combine SM+BM, because it was obvious he released his mode before going into SM. But it's also not confirmed that he can't, so we just have to see what happens.
You said that there won't be any power-ups, yet Naruto still has the power of the other bijuus. Kishi wouldn't of done that, if he didn't plan on using it...