Yes, serums are no longer as necessary as they once were to raise a woman's sluttiness and keep it high. But the premise of Lab Rats 1 and 2 has always been about using your discovery of the serums to corrupt the women around you and take advantage of their increased receptiveness to your advances, and anyone who argues the contrary is being disingenuous. At one point in its development Vren removed the mechanics of "temporary sluttiness," which required a woman be serumed up with suggestibility in order to more readily convert it into permanent sluttiness. I believe he did that because a lot of players cba to learn how temp sluttiness worked and complained that none of the women were sexable. So now we have much more easily, conventionally seducible women in the game; meaning many players (still) don't bother with serums aside from the business because now they're more hassle than they believe they're worth, and that's okay. And many don't even bother for the business because they can console themselves as much cash as they want, and that's still okay
I disliked the change, but it was Vren's game and his prerogative to change it. I have considered re-adding the mechanic in my own personal build since I liked the challenge and felt it was closer to the original premise, which is just my jam. But that's neither here nor there. What Vren did DID open the game up to more players and increased the available options for players who have a distaste for the date-rape drug angle or are otherwise not interested in drug-based corruption as a porn trope. I will always support more options