I always thought it was too bad there wasn't a loser Robert route because I think that's just the only way to make him interesting. I wouldn't really call it a "cuck" route since there's no actual relationship but Robert and Ian are already set up as a colliding antagonizing force with Lena as the "prize." Even semi-confident/competent Ian's are better than Robert in pretty much every way.
Not only do they fight (twice!) but their dates and interactions with Lena are generally right near each other (like same day or next day). In each occasion, Lena remarks how much more she likes Ian than Robert (cause Robert is boring).
A chad, or even normal, Ian has got the bigger cock (slightly longer but noticeably girthier says Lena), more compatibility with Lena, is better at sex (particularly oral), has actual career goals and a real money making career*, is smoother, better at dirty talk (the route where Lena hates Roberts dirty talk is pretty funny), etc. etc. Like it's all there but nobody ever reflects on the fact that in these routes Ian is so much better than Robert. After the second Robert-Ian fight, if Ian wins and is generally dominant, Lena describes her relationship with Robert as "a guy I sleep with occasionally" even if it's only happened once and it was not a great experience. She could have been continuing to string Robert along (refusing to sleep with him and refusing to sext with him etc), where he acts like a sad sack and Lena still describes him as "a guy I sleep with." It'd be a great place to just emphasize how much better Lena thinks Ian is than Robert and that she stopped sleeping with Robert specifically because of how great Ian is. It'd be a really cool way to get some "cuck" fetishes into a dominant route (I'm using the fetish loosely here).
Cuck Ian routes are much better filled by guys like Mike or Axel than Robert too. So it feels like Robert's only effective purpose is to be "cuck Ian" of a dominant Ian route if Lena decided to engage in a casual relationship with him. But even then, it is not a particularly fun experience. This concept is kind of there in that Lena does say things like "Ian is much more sincere than Robert" but they're really quick and never really expanded upon.
*This is really only assuming the game is not set in the US. Career waiters at high-end restaurants in the US (like the Yunalesca seems to be) can make crazy amounts of money. A first year waiter at the type of place that has a sommelier (and serves expensive wines like the ones at Yunalesca) but is not a Michelin star place can still easily make in the 80-90k range and making up into the 200ks is not unheard of for successful head waiters who have been doing it for a bit. I dunno about high end waiters in other parts of the world where tipping is less common tho.