I think people are overestimating the complexity of the game.
So far, the routes have all been pretty separate from one another and not intertwining that much. For example, Ian cheating with Cindy or not or not having any relationship with her has not been of any consequence considering all 3 variations play the same (give or take few sex scenes).
The same can be said for Lena and Ian's relationship. Regardless of their relationship status (commited, non-commited, no relationship), both of them are going to be at Ivy's party no matter what, hence not impacting the overall story.
Don't get me wrong, the game is far more complex than most but that complexity comes from the sheer amount of options you have and choices you can make rather than the overall complexity of the routes intertwinning with one another. And I don't think having 2 Protagonists complicates the story if you just think about them as 1 protagonist and 1 side-character.
It's all subjective and based on what you consider complex. Yes the set pieces tend not to change throughout playthroughs, with the exception of Cindy's party, Alison's trip, and Holly's trip. This is most likely done to reduce workload and streamline information for the characters. For example Ian hears Cherrys side of the drama of he goes to the bar with her, but if doesn't that information still needs to be communicated to him, so there are other points in the story basically the same dialogue and choices come up, specifically when Cherry is hanging out with Ian and Perry. In universe I guess both friend groups are so strong and intertwined that no actions Ian or Lena take can break up the groups and thus their hangouts and parties always happen. Lena and Ivy's friendship for example can be brought down quite substantially, but Lena still shows up to her birthday regardless.
I think the complexity comes from the sheer amount of variables though. Take a look at the variable list for ORS and imagine how many variables the average game will have on here. The average game will be a male protagonist game which probably will have individual score points with let's say 5 girls. Each decision either raises said point, lowers it, or keeps it the same. Then once it is high enough the player can engage in their route. At the halfway point or towards the end the game will have a moment where it checks all relationships and if the player is cheating then the player face consequences, unless it's a harem game of course. ORS, just looking at Ian's parts will have much more to it. To court the women you need to build up their relationship stat, but also their hidden interest stats, ian_go_holly, ian_go_cindy, Ian_go_alison, etc. Then furthermore there are variables determining if Ian is in love with any of them, which tend to be mutually exclusive. Then in bed with the girls they have their satisfaction variable, which is minor but goes a long way compared to games just a little dialogue and then some gif. Along with the satisfaction there are also the preferences of the girls, Holly being willing to swallow unlike Cindy who wants Ian to perform cunnilingus before she blows him, or Alison and Minerva hating anal unlike Emma who is an anal enthusiast.
I think it's true that the different paths don't intersect too much, but I think that's because up until this point they have been mostly Ian and Lena sleeping around. Unless you're Alison or Axel, most characters aren't getting pressed over the MCs sleeping around while they're not tied down. Only in chapter 9 can Ian and Lena become a couple and already by chapter 10, Ian can cheat with Cindy, and Lena can cheat with Axel, Mike, Louise, Ivy, and Mark. And these are marked by the game with cheating variables, meaning it will come into play later. The other routes haven't even progressed to the official couple status yet. Holly and Lena discuss Holly having the talk with Ian and hopefully that will happen in chapter 11.
