There are many different "athletic" body types. A distance runner doesn't look like a rugby player. There are some athletes in certain sports who have an "obese" BMI while maintaining low body fat but those are a tiny fraction of the population. (Most people underestimate their body fat percentage.)

BMI is accurate enough for a general population risk screening tool. We aren't dealing with precise numbers here anyway, just approximate ranges with significant differences between the results of various research studies.

On an individual level excess body fat is a critical risk factor for COVID-19.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7430889/