Well Sihil did answer that part about the NTR and routes. he said the NTR path would be a kinetic novel spiralling into the mc losing all his loved ones without having any chance to stop it. Non-NTR will have two routes, basically a more loving and a more corrupt hero one, that will be slower. Both would have about same time dedicated to it.
Now I do not really think that last is wise from a character consistency point of view or development time since seems Non-NTR would need at least 60% of development time to keep up a bit, though he at least has the magic solution to make the girls be stupid in NTR path. It would be wiser if the NTR was just as slow and the NPC would have to work as well for their sex, if needed introduce a third character that could step in if the NTR NPC would go to fast who can handle them or just kills them. Then again NTR is the ultimate easy power sex fantasy where the NTR NPC is almighty, can do whatever he wishes without repercussions and will always succeed and have the ladies gushing and dripping wet for them.
So little chance of that, but it would be nice if the NTR NPC would have to work as hard as MC for a change. I doubt though that slow burn NTR games will ever be a thing.
I mean he did say it and it does come down to that from what the last patreon messages was saying, but from the NTR path he is shown a bit of something and he does get angry and Zel does tell him to use his anger implying a fighting chance.
The game from the start already had this whole idea that there was going to be a fighting chance, which had my hopes up a bit because it would finally break from the "dime a dozen shoe horned in idea". See you are correct that the NTR NPC does have the power but here is the thing.. so does the MC, yes he is inexperienced and yes he has to learn it and so far it has been made clear he is a chosen champion. Long story short all the tools needed to be able to fight back even if he was to bide his time. See if you just learned you have powers but know that the people you are forced to work with also have that power and longer then you and wield it better then you, but hear you have been chosen and must learn and you will be able to do the same as them if not more. That is more then enough incentive to tell you that while you cannot do anything now you can work hard to make sure to be able to overcome whatever is currently taking place. It's not like what the NTR NPC has the MC does not have.
As to answer your question of " I doubt though that slow burn NTR games will ever be a thing. " . Well the answer to that is yes, yes it could definitely be a thing however that depends on the writing and execution of it. Something that that a lot of people do not even try or attempt to do, they rather be like here have some NTR for the sake of having it with all the shitty writing at it while giving you some of the most rough and raunchy scenes you can ever get which yes does make them hot and amazing but again the immersion just kills it for a lot of people. But yeah in the end it is up to him and his team what he wants to do.
Ill give you an example of a game that has so far the most decent done NTR ( not the best not good not even amazing as it still has flaws but it is going through a rework )
The NTR side of your gf in Where It All began by Ocean. Your gf ends up cheating and what not depending your actions but even then the game gives you a chance to sort of make amends or what not and there no super power involved.
The Adventurous Couple, another one again NTR is not amazing or perfectly done but still believable and you get the option to work it through and get a fighting chance to correct things.
They are not perfect but they sure as hell do a lot of a better job compared to 99.5 of the othe NTR's out there. But it is not just NTR I am against bullshit writing in general for example, if a girl is hardcore lesbian from the get go and you as a male suddenly make her dick crazed is also breaking an immersion and is shitty writing. Keep your story consistent.
But yeah I don't want this to turn in to an NTR debate as I have nothing against ntr I have something against shitty writing in general and sadly NTR is the victim of writing om almost all of these games and gets the top award of " shuved in for the sake of just shuving it in" award.
I just want these Dev's with those golden gem games to start trying something different for once in their life.