The convoluted responses of Fox and PhD are proof of your statement.
Fortunately, FTs in China are not responsible for teaching grammar.
Given their tortured struggle with double negatives, imagine the verbal discharge if they taught articles.
The horror.

I've never mentioned double-negatives myself beyond saying they are too much for me, so I certainly don't even bother with a slight effort in their direction, let alone a struggle.

I suppose Turnoi can seem convoluted sometimes but that's because he's a linguist, and linguists tend to be a bit fanatical about getting grammar and stuff right. So that's not a nasty criticism of him at all.

I like to intervene sometimes in basic Mandarin; the oral side of the language, and that's only to be helpful. Because if you say 'mei ge ren bu...you simply will not be understood by a Chinese; whereas you may be understood by a foreigner with a good knowledge of Mandarin; because he/she will make more allowances. Alas that won't help you much.