I don't necessarily agree with some of what you say here, but different people have different opinions, and that's fine. I just don't want to leave it unsaid that there's a lot of people, probably the majority, honestly, that have little to no interest in balanced difficulty or gameplay in their lewd games. You are entitled to your opinion, I am simply providing some counterpoints.
Yes, most of the difficulty is tied to the pure route, and the slut route has all the content but little to no challenge, but that ties in with the narrative. That's literally something the game itself points out several times, "Oh, geez, I can make so much more money so much easier if I just let the patrons do what they want" and whatnot. Yes, it removes the challenge, but honestly that's just what a lot of people prefer, they don't want to have to actually play the game well to get the lewd scenes, that actively takes away from the enjoyment for some people. When it's difficult to get lewd scenes in lewd games, most people don't tend to play them. Not to say that it can't be done well, or that nobody likes it, but there is a definite cause-effect between "lewd scenes are harder to get" and "fewer overall players".
And as for the stress levels, the game explained how it works pretty definitively. If your stress is high, Angel will agree to do things she otherwise wouldn't in order to avoid confrontation. As you yourself said, "if you're stressed out, it's more difficult to do things that go against your nature", and it really seems like being confrontational and/or rude is against her nature, thus she folds under pressure when she's stressed out. This is a very real reaction people have to high-stress situations, her being willing to get publicly groped to avoid making a scene when she's super stressed is one of the more realistic things about this game.
It's heavily implied that Angel has lead a very sheltered life. That's really all the reason there is or really needs to be for the innocent girl stuff, she's been sheltered by her father from all the potentially dystopic shit going on in the outside world. I never read anything that implied that the dystopian setting was so dystopic that they had like breeding pens or all women are slaves or something like that. Just a country that recently got out of a war where the majority of their female population died, and women have less rights in retaliation from the previously oppressed men. Other than that, it's kinda just business as usual, but maybe that will change in future updates, I dunno. Either way, seems a little extreme given the info we have from the intro and what we see in-game. This isn't the Hunger Games, it's an otherwise normal post-war city where the government probably has bigger problems than making sure every female in existence is a breeding sow with no rights.
If I said anything that came across as rude or offended you, I apologize. That is all, thank you for coming to my ted talk.