It is true that some muscle draining stories end up with as goreography (like pornography but with gore, gore that doesn't contribute to the plot, gore for the sake of gore).
Another common negative is when they grow past 7'6" tall or 5' wide, it goes from sci-fi or feasible fantasy into trying to one-up similar stories by being bigger, crueler and grosser.
But I almost always like the start of these stories. And some are good stories that have decent endings.
As others said, roll reversal, female muscle growth, sometimes the female drains intelligence and knowledge are good themes. So are biggness, cruelty and suffering -- but up to a point and it should to contribute to plot or character development. It shouldn't be there just to be extreme.
Probably the thing is knowing when to stop draining one guy and to move onto the next. No guy should not get smaller than say 4'11-1/2 and 98 pounds (the 3rd percentile for 20 y/o US women).
www cdc gov/growthcharts/data/set2clinical/cj41c072.pdf
I'd also say that the female should generally not grow past the 97th percentile height for US men (6'3"), because then her life would be too difficult. She'd be hunched over and looking down all the time, a submissive posture.
www cdc gov/growthcharts/data/set2clinical/cj41c071.pdf
A writer can go more extreme, but then the readership is smaller. Of course the readership is not so important for free web stories.
I say don't try to compete with each other for grossness or bigness. Instead compete on plot, emotions, character development, modeling future science, etc.
Mostly authors should follow their muse and write where their inspiration takes them.
