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.
The stat system is just a representation of Ian's personality, he's not using it to "bypass" situations(well expect maybe will points), it's just exemplifying that's he's getting more and more comfortable conveying that "vibe" to ppl, hence why he gets experience points the more he chooses specific options:
Intelligent - he comes off as knowledgeable, quick witted, and wise
Charisma - he comes of as sociable, charming, and somebody who knows how to tell a person what they want to/need to hear.
Lust - he has a flirtatious vibe, and knows how to build sexual tension between ppl who respond to him.
His clothes also factor in creating that "image" as an accessory to his personality(same with Lena).
What Ian has as an advantage is repertoire with all these women. Besides Lena and Jessica, they all know him/know about him(Cherry), so he bypasses the whole "First Impression" phase, and is valued more for his personality(i.e. he has an established connection with them). Even more so, because they know him, they already know whether their attracted to him or not. Somebody like say Axel or Jeremy is more likely to have that initial magnetism(most women in the game blush when they see Axel), but Ian is more likely to actually establish a connection because he's "authentically" sociable(think Ivy vs Lena), hence why Cindy who knows both Ian and Jeremy is way more attracted to Ian than Jeremy(hell even Alison simply wants to fuck Jeremy, but actually wants something more with Ian).
Eva's done a pretty good job making Ian's story grounded, and that probably has to do with the fact that as a woman she writes female characters with much more care. The only issue i would say is that realistically all the young women in Ian's life would not be attracted to him, not because he's average, but rather because everyone has their preferences, and he would eventually simply not meet some of them.