I'm not a costumer, and I'm not a dancer. But I've done many musicals and gone to many cons, and in both venues there are Costumers and there are Dancers. I think there's a gene for each of these, because it's a talent super-glued to an obsession.
It's easy to tell who the Dancers are in a musical. They are the ones out in the back parking lot between every number, working and working and working until they have each nuance of each step so ingrained it is instinct. And the Costumers are the ones who are pinning and sewing and building not only today's costume, but also the ones for the next several shows. And at the cast parties, the Dancers are out on the driveway comparing steps, and practicing for the next audition, the next show. At the cons, the Costumers are looking at the nuances of each other's stitchery, describing the next con's costumes - maybe the next several. And pretty often, the costumers are out on the dance floor as well.
I'm awed by both groups. I have neither the focus nor the drive nor the artistic talent to see a costume in a movie or TV show or in a comic, understand how it would look on me, then design and build it. And my dancing is strictly a "best effort" kind of a thing.