In most porn, the man with the biggest cock automatically wins, but in ORS Ian still stands a chance no matter if he's fairly average physically or not—the same way he would if he was a real person in real life.
It is a very good point that you have just highlighted, indeed, you do not need to have the biggest cock to be able to attract or be the best Chad in the world, Ian is a clear example of this, he can, according to our decisions, have a chance with almost all the women in the novel so far.
But now we must not forget that one of the main reasons why he can have a chance with these women comes largely from the fact that he is the main character, for this reason, he is surrounded or protected in situations by the plot armour ( in this case it would be the different stats or skills), which make the situation quite easy since on several occasions he achieves unlikely things that would be very difficult to happen in real life and less than an ordinary person or with a common life.
For example, if we do a run from the beginning of the novel with Ian choosing options that do not give us stat points or that are related to them, we can see how Ian's life would be very different and he would not achieve even half of the things that has achieved so far, one of them would be not getting to have sex with Alison the first time or not being able to keep her job at the magazine if we upset Minera or better yet being able to convince Cindy to cheat on Wade with him.
To close my already long post I challenge anyone who wants to test my idea and try to see how many things Ian is able to achieve or maintain without stats, in addition to clarifying that this is just my theory and anyone could give me their opinion about it.