6paths of obito== dead jinchurikis. Nagato was so successfull because knoha did not knew the power of this dojutsu. as kakashi mentioned somewhere when fighting obito that they came now with full preparations... thus madara was also shown not using them coz it was like overdoing those special powers. nagato too did'nt aweaken the ranningan at first place. it was of madara which was later used by obito.