> If you raise your arm above your head in front of the mirror, you should see your ribs, and you should see the clear outline of your latissimus dorsi. If you can't see these two things clearly, you are overweight.

This is kind of an absurd metric. You can be at ~20% BF (which is by any standard a healthy percentage - some studies show best all cause mortality outcomes in men at 22%) and still not have visible ribs or lats with one arm above your head.

Different people carry weight differently as well, no visual test like this is going to be blanket accurate.