If guidance is written in the rulebook, arguing that it isn’t part of the rules as written seems pretty asinine to me.
It's foolish to believe guidance is RAW: it produces conflicts all through. Particularly from the DMG. But let's look at just one from the PHB.
As you make your monk character, think about your connection to the monastery where you learned your skills and spent your formative years.
According to you, this piece of guidance is a rule. Per RAW, every player creating a monk
must think about their connection to their monastery. Which is delightfully ironic because that would stand in direct contradiction to another piece of guidance, which is that the player decides what their character thinks.
That is a completely made-up distinction.
Let's see...
Creating a wizard character demands a backstory dominated by at least one extraordinary event.
This is a
rule according to you, right. You say that
RAW is what's written. RAI is what they meant, but didn't communicate clearly.
So
every wizard player
must create a backstory dominated by at least one extraordinary event. And
Put some thought into your name even if you’re just picking one from a list.
DM What is your character's name.
P1 It's Hrukk the Barb...
DM Whoaaa!! Stop right there. You have to put some thought in. You can't just come right back at me with a name.
Or
People of towns and cities take pride in how their civilized ways set them apart from animals, as if denying one’s own nature was a mark of superiority.
DM So you're quickly learning that the people of this town are ashamed about the filth and crowding; they see that they are denying their own...
P1 Wait on there (flicks through some pages). Yeah, right. No. People in towns must take pride! No shame for them.
DM ...
Or we can imagine a similar exchange, say with a druid or ranger PC born in a town, but who felt ashamed of denying their nature. Which of course will conflict with other text.
RAW is - "Rules As Written". The clue is in the acronym. It's
rules (not anything else) as they are written.
In this regard, you two have gone a bit Upton Park. Let me know when we're able to continue our journey on a sane basis.