Yeah it's a good theory but I've heard this possibility someplace else.
Sasuke activated Susanoo for the first time when the Raikage used his Raikage bomb. Incomplete but still a tough defense. FRS only need to connect to then start expanding. It destroys at a cellular level and w/o the shield that Itachi had, I doubt it can tank it....I only see Amaterasu here.
And sasuke activating Susano here
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When gaara attacks him
Raikage punched through Amaterasu, not susanoo.