I think that the 2 best uses for Wardogs is Siege, and to create morale issues in the enemy.

The good thing about sieges rather than open warfare is that if you send your dogs after a unit that routes in the fields and a part of that unit survives to run off the map, the dogs will disappear off the map too. Whereas a routing unit running to a city square is merely taking the dogs closer to the other units that are guarding the square. Result.

As for morale, your wardogs should sit just behind your Infantry. Whilst it has been noted that dogs aren't too good against Heavy Infantry, the way to resolve it is to wait until the enemy hit your lines, and then release the dogs.
Your enemy will be trying to stab your front line whilst rather annoyed Dobermanns are trying to nibble their important places.

A third but risky use is against the cowardly archers that are slowly whittling down your lines, but that can be dodgy as your handlers sometimes get too close to the enemy lines before releasing and whilst dogs are respawned after a battle, your handlers aren't !!!

good hunting.