They really are quite similar the two tools.
In my opinion, keyword difficulty bases its results or give more importance to the rank and page rank domain of the page. DIFFICULTY how much has the keyword to climb positions. It lets us know the competition in a keyword internet with just one click.
SEMRush results give more importance to the organic results by keyword or average result within a given time resulting traffic keyword. not showing us so directly against whom we compete.
Both are needed and complement each other to me, but I like to read more reviews.
