First there is a huge difference between controlling and restraining/defeating something. Right now Madara and Tobi are trying to controll all that power, to make it act according to their will, which if you ask me it is a lot harder than trying to restrain it, defeat it.
Yea all the alliance barely managed to damage it, but come on, besides a couple of characters that are Hokage level, the rest don't really matter, even in higher numbers they barely stand a chance. Only after Naruto gave them a power boost did they actually make a difference.
But that is different from the 4 Kages, i mean come on, they are amongst the strongest ninjas in the history, i am pretty sure Hashirama could do better against the Juby than the whole alliance did so far, add Minato's sealing jutsu (it's safe to assume he would know some basic restraining jutsu and his FTG comes in handy as well, eliminating the Juby's bijudama) and the fact that they are now EDO and they can use thei jutsu full power, without having to worry about exhaustion or chakra.
But then again this is just a Manga, and it can go any way Kishi wants it to
