> When you write with perfect grammar and punctuation, most people don't know how to read into the nuance
I still can't understand the argument here, it sounds so off that seems fabricated to me.
When you read the Divine Comedy (we study it in high school in Italy) the grammar is not in current modern Italian, the style is from 550 years ago, the poem is written in hendecasyllables in terza rima [1], the references are often obscure, but in no point of it the tone is hard to understand, because the author conveys it explicitly.
l’ora del tempo e la dolce stagione;
ma non sì che paura non mi desse
la vista che m’apparve d’un leone.
Questi parea che contra me venisse
con la test’alta e con rabbiosa fame,
sì che parea che l’aere ne tremesse.
Dante is saying that it was a beautiful day of spring, but not as beautiful to not be scared by the sight of a lion that went his direction, looking enraged by the hunger, making "the air tremble"
Writing is a non-verbal, not-in-person, form of communication, you can't look for what's not in it.
Assuming a neutral tone unless specified otherwise, it's always the best bet.
Also, as I've said before, improper grammar could also mean "I don't know the grammar of your language well enough", if I'm writing French, I make a lot of mistakes because I don't use it very often, so the tone is the last of my concerns and the people reading it could easily think it's from a 9 year old kid who hasn't finished primary school yet.
If you think that correct grammar is more than just "the proper way to use the language" you're most probably seeing too much into it.
> Imagine you're working with a new PM and he tells you the team's progress is 'acceptable.' What does that mean exactly?
it means "acceptable"
in a scale from 0 to 10 acceptable is >= 6 and < 7
but, when in doubt, ask, words are free.
[1] https://en.wikipedia.org/wiki/Terza_rima