Ringo has the sole writing credit and George has been quoted saying it's his song. I'm not sure how much George wrote on it, but it seems like ringo did most of it (unlike some of his songs like photograph).
Either way, saying he is worthless to the band is stupid. His vocals in octopus's garden, yellow submarine, with a little help from my friends, and a couple others are perfect. Any other beatle singing it wouldn't be as good.