I've received a fair few suggestions on insights in the humanities which I'm currently writing up to add to the post. I considered some of the Scholastics but felt that they hadn't had an impact on modern thought in the same ways as most of the others (which is a relatively good proxy for "correctness", which is one component of being "great", which is a bad metric but I have to draw the line somewhere). Would you disagree?

Also, I agree that there are some amazing artistic achievements. To keep things concise, I wasn't focusing on them here (I'll make that explicit now).