TOKYO—Streaking down the track, with only six steps to go until she reached the finish line, Elaine Thompson-Herah stuck out her left arm and started pointing at the clock. She knew she had the win. It was only a matter of what else would come with it. With a time of 10.61 seconds, the latest in the long string of Jamaican speed stars defended her Olympic title in the 100 meters Saturday. She broke a 33-year-old Olympic record held by none other than Florence Griffith Joyner. And, as a more-than-fitting bonus, she revisited a debate first triggered by the fastest Jamaican of all—Usain Bolt. Yes, the gold medal and Flo Jo’s venerable record were great. But the question could not be avoided: Just as people wondered what Bolt might have given up when he hotdogged his way to the finish line in his first Olympic victory in 2008, how much …