No, you're conflating Big O measuring an asymptotic upper bound of a function with worst-case analysis measuring the upper bound of resource use. These are diff

No, you're conflating Big O measuring an asymptotic upper bound of a function with worst-case analysis measuring the upper bound of resource use. These are different things. Asymptotic notation is totally oblivious to what is being measured, whether its a worst-case or average-case or anything else. You can give the Big O of the best case, the Big Theta of the worst case, etc.