That’s because BMI is actually pretty good as a screening tool. It’s easy, simple, and pretty damn accurate when combined with an eyeball test. To the extent that it misclassifies people it is far more likely to underclassify obesity than overclassify. The people complaining just don’t want to hear it.
Anywhere from very important to not important at all, depending on your specific job.
There is some good news though, you’ve been lied to about sucking at math. Whether by yourself or other people I do not know, but the education research I have seen has been pretty clear that the main difference between people of normal intelligence who are ‘good at math’ and those ‘bad at math’ is how long they’re willing to work on a problem to ensure the correct answer before moving on.
I know ‘try harder’ sucks as an answer but it’s the best one I know of and at least in this case will actually make a difference.