In response to SonicsMonksLyresVicars' comment:
That's my point; a band cannot succeed on their own without good songwriting skills regardless of their singing/playing ability. However, a band with a good songwriter (or even a few decent songs) can succeed with even the most modest of singing (Dylan, Hendrix) or playing (many, many bands) skills because the critical, most important, most rare skill is composing.
Sure, a band/singer can buy in songs and succeed, though in rock'n'roll that ship sailed when the Beatles arrived i.e. you don't write, you got no cred. But that doesn't alter the fact that without songs you cannot succeed, but without the other stuff you can.
If people like your music it doesn't matter if you get any cred. I listen to music I like without knowing who wrote the songs. I think a large part of the rock buying audience does the same. If I like the sound, I don't care how the band got their songs. Cred has nothing to do with the actual music. It is a non-musical aspect important only to those who care about such things. I like the Archies even though I know that the cartoon characters did not really perform the songs. I could argue that proper songwriting is more Tin Pan Alley than it is rock and roll. Rock evolved from music that was not so much about songwriting as it was about adding a personal mark to standard forms of music.