Although Corbett was a revolutionary fighter - the first man to consider movement and defense. I do believe that John L would have beaten him in his prime. For the following reasons....
1. John L lasted over 20 rounds against Corbett, when he was past his prime, overweight and HUNG OVER from drinking the night before.
2. It was a close fight up until the knockout.
3. The knockout was more exhaustion and old age than Corbett bringing the pain. (e.g. Holyfield-Toney)
4. Corbett was knocked out by middleweight brawler - Bob Fitzsimmons, surely John L is bigger, stronger and more ferocious in his prime than Bob?