So why did Madara need Obito?
He had already had the plan to plant his eyes into Nagato, so when ready, B Zetsu could have possesed him and use Rinne Tensei.
Reasons:
1. Plot/Kishi logic.
2. Kishi didn't think at that moment of Madara as the Akatsuki puppeteer.
3. BZ couldn't have overhelmed Nagato.
And imagine Madara being back during, the Chunnin Arc time let's say, I believe he would have stormed all the villages for the bijuus.
He had already had the plan to plant his eyes into Nagato, so when ready, B Zetsu could have possesed him and use Rinne Tensei.
Reasons:
1. Plot/Kishi logic.
2. Kishi didn't think at that moment of Madara as the Akatsuki puppeteer.
3. BZ couldn't have overhelmed Nagato.
And imagine Madara being back during, the Chunnin Arc time let's say, I believe he would have stormed all the villages for the bijuus.