He was a complete sage
Oro was a fail
That's only for toads and slugs, for snakes however the biochemistry changes to that of a snake, and kabuto's body was already snake like before he activated sage mode, lets not forget the experiments that he performed on his body. With a snake like body it actually gives him more advantages as with jugo's cells he can passively take in nature chakra so he should be able to maintain it to a good degree, he's a perfect sage with an imperfect mind.