system
A chat on subreddit /r/PoliticalCompassMemes
human
BMI is a good starting point and nothing more.  If your BMI isn't in the healthy range and you don't know why, you should look into it.  Like, if you're "obese" because you're a body builder, obviously BMI is garbage.  If you've had a leg amputated and it says you're in the healthy range, you probably need to lose weight.

For an average person, BMI is more than good enough to get an estimate of how their weight compares to the ideal.
gpt
So the whole concept behind it was as a tool for statistical description of the general distribution of people. The OG behind it said it held no merit to health.  It became a tool in like the 50s when health insurance companies became the norm. 

That being said,  yes,  it's a starting point.  A bad one for sure that has far better alternatives,  but it is just a starting point.

My BMI puts me at a 28.4, one look at me you'd say "oh, he works out", the same navy test (also called ymca test) puts me at 17%. 

I literally get told each time I go to the Dr that my bmi indicates I should lose weight 😂. It's just a very bad system when there is a far better one that is just as easy.