BMI assumes you are the normal semi-sedentary modern person. It's not meant to be used on serious athletes or weightlifters. For 95% plus of the population, BMI is a pretty accurate metric.
Maybe not generalists, but cross-specialists to work against the silo effect. For example, someone who knew both number theory and quantum physics deeply might make some important discoveries.
Then, these cross-specialists could themselves caucus to create a kind of synthetic "generalist" viewpoint, like a Council of Experts.
We have the instinct to consume sugar because it is the most concentrated form of energy that humans can process, not because it is naturally paired with vitamins.