It won't be forced, if NTR off is an option, it has to mean NTR is off.
So look at it like this. If you cheat with NTR on, choices might mean Dylan is Ayua's dad, if it's off, Willi is Ayua's dad. Either way, AYua will exist as a Zane and can be explained in SG, without forcing the player down any path. Ayua is inevitable, but the choice of how she exists can be open to player choice, with a little bit of scripting shenanigans.
But the NTR thing, I'm just mentioning WHY Miru is so great. For the advertised NTR aspects that are a drawcard for some players, there needs to be the consequence of losing something precious. I personally am not interested in NTR, but I like the idea that there SHOULD be consequences if I get Willi to cheat on her. That will make a far more interesting story. I'll play one were Willi's faithful, and several where he isn't. Like in SG, playing one path will mean you never get all of the story - Ocean hides things that only get revealed on some obscure choice combinations, even things like different images in the background of renders. So I'll probably explore the whole lot, just to get a better idea of everything that's going one, regardless of my preference for Katie.
Sure, but Ocean wants a bigger fan base. Being able to turn it off at the start of the game doesn't mean you can switch it on or off at whim, and we've not seen all Ocean has planned. The choice doesn't exist for people who want to play with risk, it exists for the people who want to play without risk. It's not an in game choice in that sense.
That's like saying Donna wasn't really pregnant in old WiaB because we had the choice to choose to turn pregnancy on. Think of non-NTR mode as booting into safe mode; you can't do all the things a computer is good for, but you can open up your word document.