As I said, I hate it when player choice is overdone, and I see no point in giving the player the option of skipping essential content. This is a complication that adds little and ultimately only makes the game more boring. In my opinion, L&P go too far with player choice here.Hmm to be honest, i don't really see the difference between the current interdependencies, and your example? In this scenario, if another character makes progress by witnessing Sophia and Sam through the window then it is very much still dependent on player's choice(s), because Sophia being on Sam's route (and therefore interacting with him for someone else to see that) is entirely optional. So that would effectively block the progress of another character's route if Sophia doesn't get involved with Sam. Which is exactly how the game works now, for better or (mostly) worse.
Anyway, the chance with the window is gone anyway, and now it might help to think of an example for the current event. One possibility would be that Ellie accidentally sees how open Sophia is with Dylan in this event, and this could have a similar effect to her watching Dylan at the party. This could speed up the relationship between her and Dylan and even open up a better path to a threesome one day, even resolving a path of separation created in the past. It would be exactly what I said, the player gets the illusion of a choice, but the game ends up with almost the same result.