So then the logic is:
(1) America has an obesity problem
(2) BMI, a method developed as a proxy for indexing body fat, indicates that America has an obesity problem
(3) Therefore BMI is a shitty gauge of obesity 
I don't think you actually know anything about BMI.
I'm sure that after the better part of a decade in the fitness industry, I might know just a little. My point is that the BMI is a shotty, misleading indicator of obesity and being overweight. That has nothing to do with the US having an obesity problem.
Example someone who is 6ft tall and 190 is considered "overweight."

And you mention it only being accurate for those who don't work out vs fitness people.....well where do you draw the line? Completely sedentary people? People who work out 2, 4, 6 times a week? Etc....