I think Madara is being underestimated here..
The only shinobi that will stand up to Madara are Tobi, Itachi and Pain, the rest will be easily dispersed, through Mokuton spam or simple Katon techniques (especially Zetsu, Hidan, and maybe Konan)
Madara will know Tobi's techniques in and out, how to avoid / counter them, this is pretty much the extent of derp Tobi's abilities
Madara knows about the Rinnegan and what to be wary of (defend properly, etc)
Madara knows about the Uchiha and Sharingan more than anyone, and will obviously not allow himself to fall victim to Izanami, and will also be very wary of Susano'o
Madara will warm up by making an army of 25 Susano'o clones, which will take their tole on Itachi and Pein, wearing Itachi out and probably destroying a few Paths at the same time. Tobi will easily be able to dodge these.
Now Madara get's serious, calls a meteor or two in, and whips out Perfect Susano'o, the meteors will be enough to defeat Itachi (after being worn out of use for Susano'o whilst fighting other Susanoo's) and, whilst I maintain that Nagato himself could fight PS, Pein certainly couldn't. This'll be the end for Itachi and Pein, and it'll be a no where near worn out Madara vs a slightly worn out derp Tobi
Madara will win with mid-high difficulty