True. However, Jaye and MC are not-step-siblings and Mal is their not-mother-clone. They have a unique relationship as a result of their upbringing and shared history that transcends the ordinary forming of a throuple from three strangers. If devs wanted to capture the emotional intricacies of intimacy in a throuple to make it grounded in reality, then I feel like they could have chosen a vehicle with less fantastical elements and characters that were not so over-the-top extraordinary (rich/talented/perfect physiques/life-saving heroics/etc.). Given the story context and character decisions, I feel like 'MC gets the girls' so long as he follows the in-game advice about being honest should bear out.
Yeah, like I said, from a gameplay and player experience perspective it's not great.
It's speculation on my part, but it feels a bit like they didn't originally plan a poly ending, but as the story and characters developed (and since this was a multi-year process, as poly and CNM became more culturally mainstream in general) decided that it could work for the characters that had developed. But if it was added later in the dev process, some of the "in-between" dialogue and whatnot that would have bridged the gap (particularly in regards to Mel) might be lacking.
Again, just speculation on my part, and it's not unusual for writers to have parts of the story "reveal themselves" later on. It's just that for many other mediums, the author would have the chance to go back and fill in those gaps before releasing the novel, TV show, movie, or whatever. That's not something that can be done in an AVN released in parts like this without requiring people to start new games from scratch and/or getting stuck in "remaster" Hell.
Ah well. Still quite enjoyed the game, just makes my overall rating of it a little bit lower.