I am an Orochimaru fan.
How come you think summoning an expired (technically) ninja is to be his ultimate trump card?
1.-Naruto can seal Orochimaru blindfolded.
2.-Regarding raw power, even with all the chakra meant to be summoned, the shinobi alliance wastes, more than simbolically (whatever orochimaru could if asked by Kabuto) the chakra aported to Kabuto.
3.-We ought to think as Naruto manga readers, Kabuto`s justu knowledge might be if not even, close to what Oro had.
4.-Orochimaru, cannot, can not, defeat Madara. It`s all about Genjutsu and Oro is good , but not that good.
5.-Orochimaru never at least for fighting purposes (just escaping or dodging) used Kage Bunshin for numbers`purposes.
6.-Anything else?
7.-Oro, as long as Kishi wants it is SEALED in whatever dimension the sword of Totsuka matches with.