But that just begs the same question. Was Whitebeard really the strongest or did Kizaru perceive his title as wrong? Don’t forget these guys can sense power levels.
So Kizaru who could sense Whitebeard’s power level was confident he could kill Whitebeard. Similarly, Kizaru can sense Luffy’s power level, knows Luffy beat Kaido, but still wasn’t at all concerned at the idea of facing Luffy and his crew with no help but Lucci and Kaku. Lol