Competitive AI in broodwar already can destroy the best humans. AI can use strategies and tactics that human can't effectively do. Most notable is perfect splitting which changes the game quite a bit.
Who do you mean by "the best humans"? I've never heard of top-tier progamers such as Flash, Jaedong, Bisu, etc. losing to AI. In fact, I doubt any B-teamer or above would lose to an AI in a Bo3.