Hmmmmm, I like all things Everly Brothers, including "Why Worry." I've listened to them since the late fifties. On Chet Atkins's special, they sang "Why Worry" and MK was on the show too. He's also commented before playing the song that the Everlys (whom he is a fan of) recorded the song. So he must not be displeased with their version.
They are classic 'hill-billy rock' and are legends in their own right. IMO they have one of the few successful covers of MK music. Jimmy Buffet has also covered 'All that Matters' and 'Whoop-de-doo', and does a damn fine job. I guess it's all in personal taste. MK is just a damn hard job to follow.