In Olden Era, creature types not only affect Necromancy but also have different Morale/Luck caps. This leads to some interesting implications on managing Morale/Luck strategies for each faction.
I saw no one discuss it yet so here is what I found on the wiki page:
| Creature type | Max Morale | Max Luck |
|---|---|---|
| Living | 5 | 3 |
| Dragon | 5 (Min 0) | 3 (Min 0) |
| Magic Creature | 3 | 5 |
| Embodiment | 3 | 3 |
| Undead | 0 | 5 |
| Hive Spawn | 5 | 5 |
| Construct | 0 | 0 |
So this means:
Temple: 5 Living + 1 Magic + 1 Embodiment: Scales best with Morale thanks to having 5 living units. However, if you decide to learn Leadership, take note that upgraded Cavalry has a +2 Morale aura, and single-faction army additionally grants +1 Morale so you will overcap Morale. Equipping further Morale-boosting artifacts or adopt the Morale law would be heavily situational and, in fact, mostly unnecessary in this case.
For optimizing Luck, instead of learning the Luck skill, it may be better to find Luck-boosting artifacts and upgrade it and save a skill slot for something else. For example, the coin artifact is very common. It gives +1 Luck and can be upgraded with a cheap dust cost to +2 Luck, which is already 66% of your cap.
Necro: 7 Undead creatures: Scales best with Luck. You should aim to maximize Luck with the Luck skill plus Law & artifacts combination.
Grove: 2 Living + 1 Magic + 4 Embodiment: Since the majority of Grove army are embodiment creatures, learning Leadership will result in inefficiency. Your Luck is also capped at 3 so it may be better to find Luck boost artifacts and save a skill slot for something else.
Hive: 7 Hive spawns: Can learn Leadership/Luck freely without restriction.
Schism: 4 Living + 3 Magic creatures: This is the classic split. i think either Leadership or Luck is fine to learn. However, I may be slightly in favor of Leadership because the Arbitrator, Schism's main damage dealer, is a living creature.
Dungeon: 2 Living + 4 Magic + 1 Dragon: Better to learn Luck than Leadership. While Minotaur is an interesting exception, it already has a base Morale of +2 and both upgrades have a way to self-boost its own Morale without relying on hero skill.
This is my opinion for the optimal strategy whether to learn Leadership/Luck skill for each faction. Obviously it also depends on your current artifacts, laws, RNG in skill learning or simply your preferences. Please feel free to share your own opinions as well.