Freud taught that early childhood experience has a profound impact on adult life. Did anyone have this perspective before Freud? Was there a precedent? If I think of literary depictions of childhood in the 19th century, for example in Dickens, there can be great pathos, but not a psychological awareness of the consequences.
This emphasis on early childhood experience is tectonic in Western culture and we still haven't caught up to it in practice. If it really was Freud's contribution, that alone makes him great.
Another dimension of Freud is that he was a taboo-breaker, and in that sense a heroic figure. Some of the steps he dared to take are still so out-there that they can't be openly discussed. That's pretty remarkable after a hundred years.