I'd say this isn't necessarily something bad -- it's okay for some options not to be available for some MCs. Otherwise there's zero point in having stat requirements for such options in the first place, if any MC regardless of past choices can select any and either of them.
He couldn't eat out Cindys pussy the second time in chapter 10. He could slap her hard in chapter 12, but as elaborated, he did flirt heavily with other women and had Lena stalkfap. If Ian would be 100% faithful towards one woman, he is unlikely to fully get raunchy with her.
9 lust: Manwhore, fuck everything
8 lust: At least two relationships, always flirt/think about sex
7 lust: At least one relationship, always flirt/think about sex
6 lust: One relationship or always flirt/think about sex
Imo, it is bad for a sex game highly focused on the choose-your-own element, since the sex is a huge part of the point. It'll be less noticeable depending on what your path preferences are, which is likely why it doesn't bother you (to ffive specifically). But the point of design in the end is to increase enjoyment. I can absolutely see Charisma, Charm, Athletics serve their purpose for the other elements. But in the end, I see those things as there to add necessary immersion in what is, after all, a sex AVN where you want to get the character & personality you've formed into certain sexual situations. When those sexual situations are present already, on your specific path, and only grayed out because you don't imagine your character would say "I'd like to stick my hole-in-one, yuk yuk" while playing golf, I just find that silly and poorly thought out, really. Not serving much purpose.
These are more my thoughts on design in general & what the end goal is. An AVN, especially in respect to the "A", is quite different than a platformer.
Other part is, I don't believe it reflects real life very well at all either.