Hunter Steele is an honorable fighter and he’s good with a sword, but he doesn’t have The Force with him. Dark Vader is a Jedi/Sith Master and he’s proficient at using both sides of the force. He may not be able to use both at once because that would likely be impossible, but he could defeat Hunter Steele either way. Steele doesn’t have Vader’s expertise after all. Dark Vader wins.