This is the only way. "slut" is the label imposed on women who have a lot of sex. In a female-protagonist porn game where the MCs must have a lot of sex, they "must be sluts" in it, or there won't be any "female-protagonist " porn game. On the other hand, a male MC pron game where a man has a lot of sex with multiple women is usually called a "harem, " which describes a location rather than people.
Funny enough I view both slut and harem pretty poorly. Deep down I think your point about how we describe things is pointing out how society is slightly misogynistic. Slut is a slur... Harem is not. Guys have harems so it's ok, girls are sluts which is bad.
{I'm about to trigger some people} Personally I see "Harem" and I think juvenile and emotionless, empty sex. It can be done well, but is almost always is BAD. It focuses on the physical and completely ignores the emotional side of sex. There are exceptions... but generally it ends up trash.
Slut on the other hand I view as slightly better. It can have the same weakness as harem, but I personally find the writing tends to be better when it's written form a female perspective. Not saying it's good writing, just that it's not dogshit. In slut, sex tends to be physical too, but there are times, hints at the emotional side of sex which is almost nonexistent in harem.
Personally I like when sex is portrayed less like porn, and more like real sex. The more sexual partners you add the more porn it gets but the less realistic it gets.
I know I'm in the minority here where everyone wants QUADRUPLE DOUBLE G's, but I actually like a plain Jane more with a normal sized body feeling self-conscious and trying to discover sex, feeling like she isn't large enough. Or a chubby Single mother trying to date again, and feels like she doesn't have the body she once had and she is competing against girls half her age who are sluts. Or a girl who is forced into prostitution and how that makes her feel.
Wow, what a tangent I went on...