Also found wildfire far from realistic. Seen one time fire spread out in desert over ground for a half of screen. Only building/tree should burn and spread out if they are close, not wildfire in open space, especially in desert.
For me its my main tactic in taking npc towns - few fireballs from dragon = the whole town on fire. No matter how many defenders inside, all will burn. Wait 2 min - send ogres and finish survivors.
Wildfire is like a nuke, unless your opponent has lvl 20 units of right spec.