Illogical thread. One, the sage of the six paths, as the name implies, had senjutsu, so it wouldn't be a weakness on his part. Two, there's nothing that can cancel sage mode like how onmyoudon cancels ninjutsu. Three, Obito was nowhere near the power of the sage of the six paths. The Sage defeated a full powered Juubi, I don't see Obito having such a feat. Just because Obito became the Jinchuriki of the Juubi doesn't mean he's equal to the sage of the six paths. To be equal to him, you need the power that was within the sage's body (strong life force and huge chakra reserves) and the sage's eyes (the rinnegan) which you need to have mastered like Nagato did.
If anything, Nagato was the closest person to the sage of the six paths. He was part senju part uzumaki and had the sage's eyes almost his entire life.