I appreciate the human writing, fwiw

Exactly. And I don't want to encourage him to have the AI write the whole text, just to let it proofread what he wrote. It's a natural language processing tool. Let's use it for that.

There's a difference between criticizing and saying, "I'm sorry, I don't understand what you are trying to say."

And if you had to email someone in Italian, would you really do it with poor grammar? Or would you write it in English and translate it, or use a tool to ensure it's correct?

I'm not telling him to stop writing on his own and instead just let AI write for him, but there's no shame in letting an NLP tool do what it's made for and correct the mistakes you made writing in a language you aren't native to.