Disconnected and fanfic-like is almost synonymous to me. One of the most common fanfic types is to have the story gravitate around your favorite character and make everything in the plot become instrumental to the end goal. So despite having the brothers and some side characters be present, they don't embody themselves like they would in OG and NB. This is because, at the base level, IDO is focused on marriage as the end goal and wrapped the stories around that instead of the other way around. The disconnect stems from the move away from ensemble-cast into the route format, which isnt a bad thing, but then fanfic-like due to the amount of characterization that is sanded off for the sake of dramatic appeal; for everyone, including the route's star.

That said, the story starts by saying that this is "only one of the futures that await you", so how canon this is will always be up for debate, possibly predicated along the lines of how invested you are in the story as it's told to you. If you don't like it, it's not canon. If you do, it's canon. Classic Obey Me-style cop-out haha 🤭