Itachi knows his s***. Every jutsu no matter how overpowered it may seem has a weakness. This gives hope to the underdog when he faces the almighty haxed overlord.
It also base on the user too, how much power and experience He or She has, a jutsu weakness to the SO6P is a power gain to someone else lower than Him. So you also must take into consideration the user.
the main weakness of susano is that it anchors the user to a fixed possition and it does not defend under the user, so an earth based attack could be usefull against susano.
also it's a double edged blade, it consumes the users lifeforce as it is used