You still didn't answer my question. The MC calling his mom by her first name is jarring and immersion breaking, and fixing it wouldn't ruin the writing. You can have incest AND good writing, it's not one or the other
Perhaps I shouldn't have mentioned the patch along with the "fill-in-the-blanks" relationship system. My gripe is not with the incest content or calling your mother "Mom", it's with the abovementioned system.
Writing in such a way as to allow for placeholders will never produce a work with the same quality as what we have now. It happened with Summertime Saga, it happened with Dandy Boy Adventures, I don't want it to happen here, too.
Let's take a look at the placeholders. If there are places where any word can go, how will the player know what word to put as the "right" one before even playing the game? And is there even a "right" word?
"Sister", "sis", "Flora" can all refer to the MC's sister. Pick one of them and read through the following sentences:
"Hey there, [placeholder]! Feeling better?"
"Ugh, it's my [placeholder] again!"
"Dammit, [placeholder]! Why do you always have to pick the worst possible time!?"
Does every sentence have a fitting word? Yes. Does one word fit in every sentence? No. Each word has at least one sentence where it sounds off or doesn't fit at all. The correct usage is determined by context and it's done by the writer, something impossible to do when they have to leave in fill-in-the-blanks spots for players to put whatever they see fit. And if you think that one of these worlds fits perfectly in all three cases, then imagine having to write 1000 more of these. Each of them with a placeholder where the chosen word fits perfectly.
And to get back to the writing, the MC calling his mother by her name has the in-game explanation of them growing apart. Not the norm, sure, but not something that you never see in the real world. The MC calling his sister by her name isn't really something that odd. You can see what the relationships between the characters are through their interactions. They might not be stated outright, but they are made clear nonetheless through dialogue, inner thoughts and interactions.
An incest patch released by the devs would be the best possible outcome. Then we can all have our cake and eat it, too. But since it's highly improbable that this will happen, let's be content with the good writing we have now and not try to ruin it for a sub-par "solution". Lest this turn into another landlady game...