Muscle mass is directly tied to how much you use the muscle.

I'd describe it more as a loose correlation rather than "directly tied." There's the obvious example of sex differences, where a typical untrained woman will not respond as quickly to weight training as a typical untrained man of similar size. There's a lot of individual variation, too, and more recent research is revealing new insights into high and low responders to resistance training. See, for example, this review.

I learned to be less of a dick to others about this stuff when I learned I was an outlier high responder in muscle strength and growth, getting much better results from near identical workouts with some of my friends. Realizing that I was lucky helped me extend some more grace to others.

Zero muscle loss while on a signifcant calorie deficit to cause noticeable and sustained weekly weightless simply isn't possible without the right sort of steroids like tren.

The best you can do is to minimise the amount you lose with the right amount of training, rest and quality macros. Ask any successful bodybuilder after making them take a piss test for roids what their losses were for their last cut.