Agreed -- Though wish it wasn't so -- been like that for nearly ever; at first, due to target audience (Eg. To-love Ru, Zero Tsukimi, etc back in 2000s), but later, "if it works, why change it?" mentaility.
lol, even tho he pointed out about realism in the 1st couple chapters, it goes on to ignore it later w/ the grinding -- Aka. Stamina, durability, maybe maintenance (blood, etc), and so on.
Yeah, this stuff didn't happen in the manga -- Of the current Eng chapters (29), 18 was the last time she showed up.
Might happen eventually, but kinda doubtful.
Can tell, like how he has to "turn the 7 sins/flowers/whatever" into "proper brides", but he already technically failed that, since the 1st failure is/was one of the 7.
"Reason" is told in chapter 3 & expanded upon in chp 4. -- TLDR ver is:
[/SPOILER]
Anyways, yeah NTR vibe due to chap 4 & 6th could lead to "justification" of said ntr.