As far as I see it, being a free-willed ET ninja seems to be massively advantageous to Madara than being a living breathing ninja.
Madara already knew of the ET ritual, so it was well within his abilities to teach that to Obito.
Is it possible that Madara wanted to be brought back by the rinnengan techniques because otherwise there was no way that he could become the 10 tails jinchurichi?
Perhaps ET ninjas can not change - and will forever remain at the condition that they were brought back at. Therefore, this would stop him being able to become the host to the 10 tails. Therefore, he would not have the ability for his IT technique.
This means that Madara is entirely in the palm of Obito's hand, even though he is much more powerful.