Remember, regardless of Obito's power ups he still is half Zetsu, meaning he has Madaras will in him at all times, Madara will let the alliance fight Obito & force him to perform Rinne Tensei again.
Madara's nerves are ice, he will remain calm regardless... he has had 100 years to devise plans for his plans, he is the smartest & wisest of all Shinobi.