You know how Erling can really shine with Armageddon + warlords + priests + lava dragons! I've tried it myself, and the fire damage to a unit under the fire sign will be simply amazing + Fire Lord...
All the advantages of Ingvar were mentioned above... Ingvar will have the entire set of runes, and what do we have? A rune that removes all negative effects, and then darkness disappears, and light remains:smile20:!

Added 7 minutes later
I already said above that the dragons will do if they are teleported or moved with inspiration + rune of battle fury...
I won't say anything about relic artifacts, it depends on how the player collects them, but darkness definitely won't work against dwarves with light (if the player is skilled).