Since Cassie is a LI, will we get to see what she is up to in this montage. Curious where she could possibly be.
Would be pretty pointless for her since the season just ended after meeting her.

Montage of her in the jail cell again with "you just met her"?
I find it a bit incredulous that there are only the two options: completely dark, or completely nice. Manipulative bastards are outwardly nice in order to be so manipulative - they don't simply rape people out in the open.
There were times in my last playthrough that I didn't want to up and point-blank rape a girl. But partway through the story there were darker situations that I *did* want to take advantage of, but could not as the decision making process had been closed. For that reason I was completely locked into the nice path, and couldn't try and manipulate certain LIs (like with the sleeping pills/wine) to have my way with them as I'd wanted.
A real life manipulative/twisted path usually starts with nice little lies, covering up the truth, then it descends into more darker stuff. You "can't let them see it coming" as it were. If I had a choice on how to play it, I would not close the dark path so early - keep that open for choosing much later on. Or even better - make it a points based system, where you can go either way depending on how many points in each you've acquired.
You guys are really confused here. There's way more than two options. Go and play around with the game, see for yourself.

If you don't rape the brazilian girl, you can still be quite mean to her and rape-y. You can do that with anyone, really. Even on the romance route, there are ways to be toxic and manipulative.
You can also build dark points throughout the game slowly, and the max points are 20 (default might be 10, actually? so you only need 10 pts in that case, easy), so I'd guess any future scenes that rely on that will eventually open up to you. So, there's your slowburn path to darkness. I'd have to look, as I'm not entirely sure how darkminded variable works with scenes outside of dark route.
Think about it this way: dark MC has a Brazilian girl all alone and vulnerable with him out on his boat in the lonely ocean in the middle of the night... you're telling me dark MC isn't going to take advantage of this perfect situation of power and control he is? And as for Nicki, it's similar but a little different; the woman he's had a strong infatuation with for years, who has been with a man that has made Guy feel small and pathetic, is finally alone with him in his condo, and he doesn't take it? A Guy that doesn't take either option really doesn't fit what the dark route specifically is obviously going for.
And on top of that, there are flavors of the dark route where your MC can be regretful and apologetic.
It sounds like what you guys want is the domination/dark corruption route, which is still definitely in the game. Afaik, you don't have to rape nicki or brazilian girl in order to get access to it, I'm guessing you just have to make choices that give you dark points, i.e. push for anal and don't be nice about it, insult, smack around, etc.
It makes sense from both the perspective of the character, but also from the perspective of the developer. It's already a very complex and open game, isn't it? I'd say it's far more complex and interesting than any VN I'm aware of out there. Doesn't really need the silliness of letting you go dark rapist at a moment's notice when your MC's thoughts in the meantime have been tame and normal.
EDIT: Also, Ashe's date isn't in the current updated game, yet. So, what you experienced might be unintended, or the author agrees with you and has changed the script. You will have to wait until S1 is complete and then you will find out what's available to you and what isn't.