People overate Minato so much it really pisses me off. FTG is not the most powerful, bestest, awsomest, most unbeatabalist jutsu in the Naruto universe. Itachi has the sharingan and could see were all the seals for the FTG are so he wouldnt be easily surprised. Itachi has good speed and great reflexes so he certainly isn't helpless without the protection of susanoo. Plus Minato would have to avoid Amaterasu, Tsokuyomi, and the Totsuka sword. All of these things are 1 hit KO's for Minato. Bottom line is Minato has nothing to counter the MS techs, susanoo in particular, besides running away.