Miles is arguably the most influential musician of the 20th century, period. While the Beatles were indeed a "global phenomenon" so was Miles (his success was hardly limited to the US). Whereas the Beatles indeed sold more records, Miles was a musicians musician who helped vanguard a half dozen subgenres of jazz (and jump started the careers of dozens of others who eventually became giants in the genre, as well as crossover successes like Herbie Hancock, Tony Williams, and Marcus Miller) his influence extended well beyond jazz into pop, funk, rock, hip hop, punk, hip hop and on and on. Even metal bands like Helmet and Mastodon name check him.

Often the bands/artists that have the most impact on the actual direction of music aren't the ones who benefit the most commercially from it.