As for 0.8.7, dark dwarven flame cannon is still rather useless, especially considering of being tier 5 unit, it has way too small range for a siege unit, considering is rather weak at only 90 hp, slow as being a siege, low rate of fire and taking 4 pop space. I know that in original they had less range than other siege, but with range upgrade they could outrange towers. Now without the upgrade, flame cannon is basically useless, a melee unit could easily reach them before they could even fire! Hellbore has many of these issues too, but they are less prominent, since is a tier 4 unit, hits air and has slightly more hitpoints. But it needs a rebuff too, because they are dark dwarven special unit too. These two units have much less survivability than other siege (including manticore), just because the range.