So here are some facts about Shisui Uchiha and my theory on how strong he could be if he were to grow up.

Shisui Uchiha has always been praised as one of the most talented members ever since he was little and he was even praised as the strongest uchiha of his time by Danzo.

Shisui’s Genjutsus were the strongest especially his Kotoamatsukami which is a genjutsu in which he can control your mind without you even realising it, it was so strong that Shisui believed he could control the entire uchiha clan to stop the coup.