Sometimes, yes, I absolutely agree, maybe even often. Not all songwriters, as great of a performer they might be for most of their songs, are the best performers for so many of their own songs. Good examples are Hallelujah by Leonard Cohen (Cohen after the first 3-4 albums wasn't IMO the best performer of his own songs) and Jeff Buckley's version; lots of Isaac Hayes' versions of other peoples' songs, most of all By the Time I Get to Phoenix
but the best example I can think of is A Song for You, written by Leon Russell, but Donny Hathaway takes it to a completely different fucking universe and makes it his own. That song is heartbreaking performed by him, Jesus.