The young Cassius Clay was simply in one of those rite of passage bouts when they learn a lot and the opponent is a lot more awkward than originally envisaged.
Cooper had an excellent natural hook & Ali was vulnerable to the hook as we would see throughout his career. Cooper also lost by KO to Patterson in 4 so while he gained lifelong respect for dropping C.C. his hook was not like the Walcott hook that KO'd Charles cold & dropped Marciano in the 1st rd of their 1st bout. Ali had a great chin as we saw in the FOTC when Frazier unleased his monster hook in the 11th & 15th. Credit to Cooper who had that moment