I don't know if people are thinking through a dog versus walker battle.
Typically, a canine's attack is designed around causing enough damage that the victim weakens due to a loss of blood. Also, when a person is attacked by a dog, most of the victim's efforts are defensive, in trying to block the attack in some way.
A walker, on the other hand, will not take a defensive stance. Since we have seen them eat a horse, we can assume they will eat a dog should they get a hold of one. So a dog attacking a walker will meet an active attack.
Yeah, but as a thinking predator, canines can be balls-to-the-wall wild, but if you have ever watched some dogs fight, they actually jump around--a strategy, if you will, to avoid being hit or bit while attacking. It is an instinct of species (even if all dogs do not employ it when fighting).
A dog attack on a walker could go in the dog's favor, as they are still operating with a truly functioning brain, and are natural fighters/killers. Not all humans are born with that.
Take away whatever skills a living
human may possess, and a walker is just a thing clawing until it gets something in its mouth with no tactical advantages.