The blind elf gives a throwaway line explaining why the MC can alter themselves so easily. That serves a purpose of explaining in-story why we can't give Brint two dicks or turn Cait into a cat/bee hyrid, or even possibly why Ryn can't get a vagina
That line is null and void with the explanation of Arona's dick. Regardless, Ryn can personally meet the goddess of fertility whenever by going with the PC. Just ask her for a vagina. She also transforms just fine when you give her items to make her tits and ass bigger.
And I think outsiders becoming high status in a culture that is isolationist and/or have been ruled by one race for centuries is generally a shit trope and shit writing.
...Do you know what game you're playing? And you're complaining about shit writing? Regardless, the MC is a somebody. They are quite literally the hero of 3 settlements, a city, and seemingly another city whenever KM finishes. Maybe even another with Tychris. The royal bloodline for the elves doesn't even exist outside of Ryn and her sister IIRC so it's not exactly like she has any options for keeping the bloodline pure or whatever nonsense. Complain about it all you want, but there wouldn't be too much civil unrest if Ryn had a baby with the savior of their people, outsider or not.
Then being able to fuck Gwyn literally on top of Garth while he high-fives you and offers you pointers also constitutes a player option.
The MC has a literal harem of catgirls. They can have a harem of 3 incestuous cow wives. They can fuck and impregnate half the women they meet. They can romance a whore to give up the anal virginity she's been saving for someone special(even typing that sounds ridiculous). They can be the champion of every settlement they stop by. They are the only ones doing anything to stop the BBEG. Almost every single person they meet is down to have sex with them.
This game is already a power fantasy, even if you choose to not indulge in half of those things. Because at the end of the day, you're still the big hero going around kicking names and taking ass.
And yes that literally does constitute a player option as long as it isn't forced.
My point is to not limit options, just make so they're not flimsy or afterthoughts.
Literally nothing determines what is flimsy or an afterthought besides how much effort gets put into it when it comes to something like this. If the option has just as much content, how is it either of those things? I don't even know how it could be considered an afterthought when it's just the most logical train of thought for many people. "I'm playing a game in a universe where people can change their genitals and bodies. I want to have a baby with this NPC and vice versa, but they don't have a vagina and I don't want to be the one to get knocked up. Said NPC also knows the literal goddess of fertility. How could I possibly have a baby with them?"
is there really anything wrong with a character being fine with the way they are?
Well first of all Ryn already gets transformed for the player's benefit by making her tits and ass bigger so there's already precedent for her doing stuff like that. Even disregarding that though, that was never the issue. If this content wasn't planned, nobody would have issues with not being able to give her a vagina(or at the very least not to this degree).
Instantly writing off a surrogate parent as cuckoldry is really weird to me
You are asking/acquiescing to your partner having sex with someone else. That's textbook Netorase, you're WILLINGLY being a cuck(wittol for most accurate definition). Sure it serves a purpose, but at that point just adopt a kid. Better than just one person getting shafted and you'd actually make someone else's life better.
