If all it takes to obtain the Rinnegan is the combination of Senju and Uchiha DNA, why didn't the Rinnegan activate right after Madara implanted the Senju DNA into him?
He needs EMS to get rinnegan eyes but a near death experience is needed. Obito had rinnegan techniques, he just needed one rinnegan to
control the statue well. (Like he fid against darui's squad)