the vast majority of pop music in the 60's would fall under that umbrella of "didn't write their own music". Hell, Elvis didn't write most of his own music, couldn't play a guitar out of a wet paper bag (was mostly just a prop), but he was still incredible in front of an audience and on vinyl.
I'm not defending boy bands, but to rule them out based on whether or not they wrote their own music or played their own instruments seems a bit naive.