The point of using gloves are to protect the knuckles as well as the person's face. On human body face is the place which has the most strongest bones. At the same time it is covered with only a thin layer of skin. Most of the body bones are protected with muscle but obviously face hasn't. Also we can improve the muscle strength of any other body part but not the face. If you hit a man bare knuckle on his face there is a high chance of busting your knuckle.

On the other hand, I dont think at that time none of the bare knuckle fighters were at the their highest point of training. May be a few but not all, if they had the same facilities like now they would have killed one person in 1 or 2 rounds. Now days boxers train very hard, using many gym equipments to increase their stamina, strength and power.

Just give this a thought, what would hurt more getting hit by a regular baseball bat or one wrapped with cousin?