For starters, whose to say that it took shisui a decade to reactivate his MS?? He may have been able to do it alot more frequently, like itachi, kakashi and sasuke use theirs... Tho it may have more of an effect on his body like the way it effects kakashi,or possibly worse... or maybe shisui rigged his eye like that after he died, so that it could only be used once a decade... And just to throw this out there, not everyone could use hashiramas cells, just cause danzo and yamato could, think of the dozens that died when oro planted them in their body... just cause shisui was a genius like itachi doesn't mean he could handle hashiramas cells... and now onto the battle, we dont know enough about shisui to know what he can do... but itachi on the other hand... i mean hes the genius of geniuses lol he broke edo tensei!!!