It's still very readable to me. I'd definitely proofread more if I were him but no need to be so harsh (I don't know if English is his first language).

It was overall a long and well written post, with a clear structure and insightful content.

Also, the article could have been spotless grammatically speaking but utterly uninteresting - I would certainly enjoy the opposite more.

The message is more important than the technique at the end of the day.