To say Metallica is not legendary is to ignore reality. By the end of this year they will have passed 100,000,000 albums sold.
While Zepplin, Black Sabbath, and The Beatles may have paved the road, Metallica turned it into a Super Highway.
How many albums did Led Zepplin sell? It was over 200 million at last count from what I heard on TV the other night about their new DVD that is out. I would say that speaks for itself.