That was Darwin’s insight, yes, but we now know a lot more than he did. It’s been suggested that some traits persist that are neutral because they’re genetically associated with other traits that are positive. For instance, the gene that gives light skin, an advantage in regions without much sunlight, might also increase the tendency to have blue eyes. The blue eyes themselves may not be helpful—they just “come along” with a trait that is.
None of that has anything to do with an animal sprouting wings.
“For instance, the gene that gives light skin, an advantage in regions without much sunlight”
How is light skin an advantage in regions without much sunlight?
How was it determined that this is an advantage?