BMI isn't really reliable on a individual level as it doesn't take body composition into account. Athletes are generally "overweight" according to the BMI cutoff.
That's generally untrue. Winning endurance athletes are almost all in the normal BMI range. You'll only see "overweight" (by BMI) athletes in certain sports such as weightlifting and (American) football which require huge bursts of muscle power for only a few seconds at a time. Those are also the athletes who unfortunately tend to gain a lot of fat and have many health problems once they retire from competitive sports.