The problem with cutting your teeth on originals is, you haven't paid your dues. If you get some experience playing other peoples' stuff, you develop a more well-rounded approach to your instrument. That isn't to say it isn't possible to create good, original music just based on your own creativity. There could be an "unsullied" player who comes up with original stuff so innovative, so fresh, so unique that the world just has to hear it. That happens sometimes.
But what usually happens is, players who go right to only playing their own compositions just don't develop much chops. I was a snobby "originals only" guy at one time, and I'm ten times the player and singer now than I was back then.
Let people flame all they want; it takes a lot of work to get down the feel and style of many other musicians.
Jimi Hendrix was a unique, original voice, and he'd tell you he spent about a billion hours playing Albert King and the like before we heard one note of him.