I think the strength of the dwarf army should be measured not in dragons, but in level 6 creatures. On this map, it is best to fight either defensively within the city or by attacking a city where the AI's stack mobility is also limited by the walls. Dragons have average initiative and are easily trapped by a wall of swords and crystals (and upgrading summoning magic is not necessary), and then they are shot down by archers and hero attacks. However, Earls and Jarls in large numbers are a very formidable and mobile force with their very inconvenient first ranged attack.