Every single action made was done by Obito in Madara's name. You said Nagato and Danzo got better build up as final villains? I'd agreed if it wasn't for the fact that Obito revealed himself as the leader of Akatsuki the same chapter we see Nagato/Pain's face revealed. So you already knew Pain wasn't going to be the final villain regardless of how good of a final villain he would have been. Danzo never came off as final villain material to me. He always seemed like a side villain. And while it's shocking on how quickly his reign of terror was, he's barely relevant to the story anymore.
Every buildup from Madara's name was put on Obito as Fakedara. Then when it's war time after every plan is near finished and complete, Kabutomaru unveils generic super boss Madara. He basically takes every buildup plot that was put on Fakedara and uses on himself.
The Izuna and who Tobi really was stuff, barely started until we learned Madara wasn't Madara. Obito as Fakedara still got build up as the final villain until then. No matter what argument is said, the villain Kishi was grooming as the final villain since after Deidara's death was scrapped and pushed aside for another, that just took all the stories and myths they were putting on Obito as Fakedara and put it on him, and this guy's been dead all the while Obito worked behind the scenes getting things together.