Also, don't confuse exploring the map with savoring it. You can explore a map very quickly. But savoring (repeating monotonous actions in the hope of getting or prolonging the pleasure) takes a very long time. It's better to play 2-3 games.
On a frozen map, I had a dwarf with 500 lava dragons and similar other units. I'll have to take him down with 20+ bone dragons plus leveling up the hero. In this single-player game, the catapult will become an indispensable thing....
By the way, in this specific case, skillful defense + evasion for the same 4 perks will give a much greater effect than killing 20% of the creatures. Killing works as a simultaneous reduction of the total damage of the enemy and a reduction of the total survivability. So, the reduction of survivability (total HP) should be ignored, because your own troops or chaos will still be very ineffective in breaking through, and the dwarf will deal most of the damage himself from darkness, on the same scale as without artillery/defense. And in terms of reducing damage, skillful defense works better, because -30% is more than -20%. Out of 500 dragons, 150 are consistently out of the game, imba-defense! :)