(The Voice of Reason) writes:
There is if you're losing as much muscle as you are fat, or more.

The more fat you have to lose, the less muscle you'll lose even
without exercising. Plus, the fat/muscle ratio is mostly genetic
anyway. Yes, exercise is important, but for dropping fat the ONLY
thing that counts is caloric deficit, and it doesn't matter how you
get it. In fact, too much exercise can be bad too.

A pound a week is an excellent loss rate, I don't think muscle loss is
even an issue at that rate. 4-5 lbs/week and I'd worry.

so they lose all their muscle, their metabolism plummets,

This is so wrong, you've just lost all your remaining credibility.