Same, we must be about the same age, but interestingly I had the opposite experience there. That newly added section was only partly the essay and the other part was grammar. I got a pretty mediocre score on the essay and thought it would bring down my score but I did perfect on the grammar and got the full 800 points for the section.

In addition to disability issues you point out, I would expect that there was also a very strong racial/class correlation with that section. I'm from a middle class white family and my parents both went to college and speak "proper" english with minimal slang. I didn't study at all the for the grammar section and just chose the option that sounded right to me and I aced it. I'm sure it was more difficult for people from communities that speak different dialects/vernacular.