This is a tired argument. Most people who have BMI in the obese range do not have one of oft-cited exceptions that make BMI an imperfect measure.
Everyone knows BMI is imperfect at this point, but the number of people who have BMI in the obesity range yet have healthy body composition is very small.
Indeed.
BMI is the best thing that people can readily calculate with easily available equipment (a tape measure and scales either at home, gym, pharmacy, etc) plus some relatively basic maths or sticking the numbers into a website.
Measuring body fat using calipers is better but hugely error prone. Similar for waist/height ratios. Body fat scales can be wildly inaccurate.
BVI is far superior but very few people have access to the equipment needed to measure that.
So we're kind of stuck with BMI as the best "simple" measure.
I say this as someone who did enough weightlifting to be in the overweight BMI range with a low percent of body fat (no steroids involved). Trust me when I say it’s a lot of work to get there. It’s not a category that includes a lot of people or invalidates the measure.
I know very fit people that still fall well in the BMI 20-25 range. Most around 23. You have to be very focused on natural bodybuilding for years if you want to become an outlier on BMI.
Or some combination with being super short or super tall. But this again affects a tiny minority.
But being obese is a higher BMI than overweight, and the bar is actually quite low. Lower than most people think. A lot of people think they're overweight, but they're not, they're obese.
Health risks of being overweight are very well researched and are significant (cancer risk, type 2 diabetes, cardiovascular health). If you meant the mortality, then it is also worse for overweight people when confounding for smoking and reverse causality.