He's supposed to have some flexibility- but he is designed like one on a lot of levels. He's not a very satisfying male MC.
Too tiny and he doesn't get good scene content. The game is mostly focused on Lena and corruption. The men who can cuck him are larger, more attractive, have better scene content, and awful personalities. He has one 3some in the game and it is sharing Allison with one of them. A lot of his content is jerking it to pics of better men fucking his potential LI. If he shows interest in more than one woman he basically gets kicked out of their route content. Hell, every rotation one of his scenes is literally just the same art as two other generic male characters who can get swapped out for him.
Game is heavily focused on Lena. Ian is an afterthought- and he looks like a little bitch.
Yes, Lena is getting a lot of corruption content + some threesomes with female characters and now first thresome with male character (not with Ian of course). And only "threesome" scene for Ian is indeed only MMF (because Jeremy is such a good friend)
You can try to play more "dominant" Ian (and fuck aroung).
You can "not corrupt" Lena, as well, for sure. Though it's extremely difficult in regards of Lena "finances" then..
But what is annoying that he is still has to depicted as weak even if you will invest all your points into strength (in chapter 10). You can't win in sparing against Jeremy in latest update (even if you have max athletics) - because plot requires you to be weaker (you can "not loose completely" at least, I guess). You have to be "afraid" of Alex despite having max athletics - because plot still requires him to be a threat. And it's already chapter 10 and you for sure can max out athletics at this time in game.
I don't think, Ian is complete afterthought in the game - but he is not main character on equal terms with Lena for sure. Most likely he was added as a "route" for "not corrupting" Lena.