Thing, which provokes most of NTR rants, is that Davide can immediately fuck girls, while MC is advancing in slow steps...
Maybe, but I'm not fully convinced.
Yes, there is next to no warm-up phase with Davide and the girls. But from a story perspective it makes sense, because the MC is coming home into a situation which goes on for quite some time then, with the family settling in and Davide becoming the center of attention. Davide sure has a head start, considering he is the main target for dad's investigations. Seen from a storytelling point it would make sense that our hero gets into this situation mostly neutral, seeing his relatives from a former point of view as his intact family, but getting really fast to the point where he sees that his whole family embraced the gangster scenario and even his beloved mother and (formerly) innocent little sister already got corrupted in the month before his arrival. It would literally only take days for his mom talking to him like "oh sweetheart, glad you're back, it's horrible here but we had to do it for your dad" to seeing her getting screwed in the shower by Davide, slowly realizing that his family maybe embraced their new lifes a little bit too much.
On the other side, the love route, it would (and should) take more time to get into any action. It's the same basic scenario, with the MC getting back home and finding his family mostly disgusted by the situation Dad brought them into. Cassandra seems to like the idea of a gangster life, but Mom and Alexis don't like it. So the MC can become their hero in shining armor, saving them in various situations and slowly turning their gratitude into desire. This way needs time because it starts the moment the game begins and not some weeks or months before.
Yes, I'm streamlining here, the game has enough rough edges and illogical points, especially because there is nor hard cut between the love route and the corruption route. There is no reliable behavior of the characters because most timed events are reused the same way over and over again. Especially the older scenes like mom's morning coffee or the sister's kitchen events are mostly unchanged from the beginning and not reflecting any significant change in the story and how you develop your relationship with them. But still, the underlying concept is visible, and hopefully saddog will come to the point where he can branch each and every scene according to the path the MC took.
But even then it should always take longer on the love route to get into action than on the corruption/NTR route, at least IMO.