Yes, "weight" (and it's close corollary, BMI) is a poor and overly-simplistic measurement of health (being unhealthily overweight), but it has the advantage of being simple to measure (thus the ubiquity of bathroom scales).
The somewhat more sophisticated idea of whether one is unhealthily overfat at first sounds both like feel-good semantics and implies measurements one can't easily do in a bathroom — but it does have an easy way to track: waist size. Not only does that serve as a good proxy (esp. for men) as to fat retention, it directly ties into another indicator we're all painfully aware of regarding weight/fat: pants size. And, with a sewing tape, it's easy to do. I might give it a try.
(Also of interest/note is the suggestion to waist size measure monthly, so as to avoid the angst of daily or even weekly fluctuations around all sorts of other things going on, inside and out.)
“Overfat”: The Health Case Against Bathroom Scales – The Atlantic
A proposed linguistic change could temper a cultural obsession with body weight.
So where's the line between 'overfat' and obese?
I have never put any stock in BMI. Most people would look like concentration-camp survivors if they complied with what that bogus index required of them.