I would rather see something on body fat percentage. BMI is not an ideal measurement in terms of health for a lot of body types.
It might not be a precise measure for some individuals (athletic, heavy muscled males) but what percentage are those in the context of a whole country ?
As an average/indicator over a large sample is perfectly acceptable, in my opinion.
Some groups of athletes list overweight because muscle is very dense - BMI doesn't distinguish between muscle and fat.
However, this does not mean that BMI is useless even here - overweight athletes often suffer similar medical conditions as overweight people generally.
Most people are not athletes. Most people do very little exercise. When using BMI for an individual you ask them if they do any exercise, but for populations it's fine.