Ed Sheeran
Ed Sheeran's songwriting is incredible, but his vocals and his overall look are... not. He knows how to write a hit, and thankfully his marketing team knows how to execute it. If he was still on his own, he'd probably never make it out of local open mic nights.
Madonna
Madonna didn't build her empire based on her musicality. She knew how to market her fashion and her brand, but her vocal skills are kind of boring. She still tours today, and it's a little hard to watch.