One reason for the “obesity paradox” is that fat located subcutaneously instead of centrally (inside the abdomen) doesn’t not cause disordered metabolism.
You have already pointed out the waist-to-height ratio.
People who have high BMI and not muscular can be safe if their fat is located outside the abdomen such as the lower body. That’s a lot of people…but there are also a lot of people with high BMI which is centrally located.
Wendy