Sometimes the Lead Sled Dog is the star. Sometimes not.
An example of The lead Sled Dog as supporting actor is Danny Glover in the film, "Lethal Weapon." [Glover is obviously a first-rank star in this film, and is fully the equal of Gibson, but I'll treat him as a supporting actor just to make my point more clearly.]
Granted, Gibson is the box office draw, the protagonist, the handsome, driven guy who makes things happen. But the Lead Sled Dog? Nope.