Does it matter anymore? Hell yes! He introduced mainstream America to the music of Big Mama Thornton, Little Richard, and blues:
Forget the cape and jump suits, the awful movies, ridiculously up-tempo covers and chestnuts, that was debris of a career squandered by, well, I'm not sure what. Ennui, laziness, bad management decisions, drugs, all surely played a part.
When Elvis mattered was in the beginning, long before most readers were born. In '50's America, pop music was, among others, Rosemary Clooney, Patti Page, Perry Como, and what at the time were already slightly past their sell-by date talent such as Sinatra & Crosby. Country was pretty mannered and predictable, with a few exceptions, notably in the bluegrass & hillbilly genres trying to do something original As it was, the "country swing" of the time was probably the most revolutionary thing going, with Spade Cooley here in L.A. and Bob Wills from Texas pushing the envelope, with distorted guitars, and bluesy vocals.
R & B of the time got little radio play except for the "Race Stations," but there was some great stuff. T-Bone Walker and others were bridging the gap between Cab Callaway & Louis Jordan and the up and coming blues performers like B.B. King and others.
But white kids in America were largely oblivious to that. Until Elvis. From Wikipedia:
During a rehearsal break on July 5, 1954, Presley began singing a blues song written by Arthur Crudup called "That's All Right". Phillips liked the resulting record and on July 19, 1954 he released it as a 78-rpm single backed with Presley's hopped-up version of Bill Monroe's bluegrass song "Blue Moon of Kentucky". Memphis radio station WHBQ began playing it two days later, the record became a local hit and Presley began a regular touring schedule hoping to expand his fame beyond Tennessee. However, Sam Phillips had difficulty persuading Southern white disk jockeys to play Presley's first recordings. The only place that played his records at first were in the Negro sections of Chicago and Detroit and in California. In the South the hillbilly disk jockeys refused to play him because they said he was singing "darky" music. However, his music and style began to draw larger and larger audiences as he toured the South in 1955. Soon, demand by white teenagers that their local radio stations play his music overcame much of that resistance and as Rolling Stone magazine wrote years later in Presley's biography: "Overnight, it seemed, "race music," as the music industry had labeled the work of black artists, became a thing of the past, as did the pejorative "hillbilly" music.
In other words, white kids had never heard a white guy sing with such raw feeling, such abandon. And they loved it! And that's why we never forget Elvis.