"If a rando fucks them, it takes the pleasure away" bro you're playing a NETORASE game... by your logic 90% of the game scenes have no pleasure. Don't just brush off the fact that this is a netorase game. Even if you, and others, like the artist, it doesn't change the fact that this game revolves around netorase, which is literally a genre about enjoying the act of sharing your love interest with others (in other words, a genre about CUCKOLDRY).
And about your claim of "updates without nts stuff". Every update contains nts because the moments where the mc and ammie are bonding and have cute interactions are literally building up the actual nts. Their love for each other is what makes it hot when she is shared, so building their relationship is totally in line with the nts course. Whereas an oyakodon would literally serve no purpose to the plot and would feel like filler, unless the MC isn't the man who is involved.
Also the MC is into netorase as well. So, if its a literal blessing for him to fuck Ammie and her mom then it would be an even bigger blessing for him to watch his wife and her sexy mom get fucked by another guy.
Edit: post-comment clarity has hit me and I realized this debate is stupid af since the mom hasn't even showed up in an update yet. Just gets on my nerves when people start pushing for vanilla shit in a ntr/s games tho.