I have no problems with Elvis' authenticity. He was an all around entertainer, music, movies, nightclubs. He had a good style and some sisters as his backup singers.
But my reservation is that Willie Mae Thornton wrote and first recorded "Hound Dog", and never received one thin dime in royalty from the man with the purple Cadillac. He was buying his momma Cadillacs while Willie lived in abject poverty. I'm sure if you asked him about it, he'd say "Talk to Colonel Parker, I don't handle that."