6. All You Need To Do Is Cardio.
Not quite accurate. Cardio is important, absolutely. But, so is conditioning and strength training.
Most professional athletes do not just play their sport. They do cardiovascular conditioning, strength training, movement prep, and muscular regeneration. All of these components round out a program to improve performance.
Runners often find their times improve when they introduce strength training into their workout regimen. Repeating the same stimulus in the same movement patterns can lead to a plateauing of results, or — even worse — chronic or overuse injuries.
Cross training (i.e. mixing up types of activity) is key, because, you have to constantly challenge the body in new ways in order to continue getting stronger, leaner, and all-around fitter.