"a dude like Schwarzenegger is probably well in the overweight category"
For illustration, Arnold was 107 kg at 1m88 at his prime, giving him a BMI of 30.3, which is clinically obese. But yeah, LOL at all these people with 130 cm waists going 'BMI is useless'.
BMI still isn't great for fat people. An active fat person is going to have a significant amount of muscle compared to a sedentary fat person at the same body weight - just doing things carrying around that weight will build muscle. Some health markers, this won't matter for - your heart doesn't like pumping blood to a 300lb body, whether that's at 50% BF or 8% - but for a lot it does. Lipids, insulin resistance, etc. are going to be quite different in someone at 40% BF vs. 20% BF at similar weights with similar genetics.
Unfortunately it's not so easy to get a good BF%. BIA scales are probably what most people have access to, either at home or at their local gym, or calipers, but both are very inaccurate at getting totals and at best can help you understand trend directions. There are places to get cheap DEXAs in a lot of cities these days, but not everywhere, and $30 each time you go is still expensive for some people.
BF% and FFMI are both a lot more useful for everyone than BMI.
For illustration, Arnold was 107 kg at 1m88 at his prime, giving him a BMI of 30.3, which is clinically obese. But yeah, LOL at all these people with 130 cm waists going 'BMI is useless'.