Some infographics will help here. BMI is terrible as it negelcts muscle mass. The vast majority of the populace have under developed lean mass in combination with too much fat.
I still think around 13% body fat is ideal for men, but it is hard/expensive to measure. Around 27% is ideal for feemales. I agree that it is beneficial to have low waist, which why waist-to-height/hip/shoulder ratios help. With the terrible hormonal profiles we see today(God help us), people are both fat and they store the fat at the wrong place. This is bad in three ways. too much fat in general, too much fat in the wrong places, and often too little fat in the right places.
I have a pet theory that you tend to store more fat in the places you exercise the most. If you start training breast muscles like crazy, I suspect you will get more fat stored in that area. I have not read any studies on this, but It seems to be correct based on the women I have gazed at the goym.
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If you get fat enough you end up looking like Arthur Leigh Allen.