The thing is if you get lean without having put on plenty of muscle first, you'll look like a bag of bones, which is neither healthy nor aesthetically pleasing.

You wont look like a bag of bones unless you start to literally starve yourself into underweight levels, like BMI less than 17. Healthy weight people at around BMI 22 don't look like bags of bones, they either have significant amounts of muscle or fat, that is roughly the level where most athletes are so you either have that amount of muscle or the equivalent in fat or somewhere in between.

BMI is pretty meaningless without taking into account body composition.

This is not necessarily true when you are young, but after about age 35, it gets harder and harder to outrun the kitchen.

It’s still true when you’re young! Youth compensates for bad diet, but it also accelerated the positive effects of good diet & exercise.