Bronco is Spanish for "rough" or "untamed" — specifically the wild, unbroken horse of the American West. As a dog name it carries frontier energy deliberately: big, physical, unpolished in a good way. It's not a name for a lap dog. It's a name for a dog you actually work with or that covers ground beside you.
The Western Aesthetic
Bronco sits with Ranger and Wrangler as names that invoke open land and physical activity. The owner profile is usually someone who spends time outdoors and wants a name that fits on a working ranch as naturally as in a suburban yard. Australian Cattle Dogs are natural fits.
The NFL Connection
Denver Broncos fans have a team loyalty dimension available here that purely Western names lack. The name can signal where you're from as much as what aesthetic you prefer.
The Counter-Reading: Very Specific Vibe
Bronco commits fully to one identity: rugged, Western, physical. If your lifestyle doesn't match that image, the name reads like a costume. A small apartment dog named Bronco produces a cognitive dissonance that some owners find funny and others quietly regret.