You’re not really understanding Kaidou’s character in this flashback… Oda has been showing that Kaidou, in his youth from 15 → 17 → 21 years old, was already able to match Xebec, Roger, and Garp, and 10 years later he became stronger than ALL of them. Man, you’d have to be truly dumb not to see this. Kaidou is the WSC; his growth in strength is superior. For example, a 10-year-old Kaidou is EQUAL to a 25-year-old Roger.