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So, there isn't a single example where luck can help achieve what morality cannot... :)
New here? I'm Roha — want a quick tour?
Well, if you're fighting a very large stack of griffons, luck seems preferable to me. :D
Here's an example... 50 blessed harpies attack five black knights with luck, either once or twice in a row.
In the first case, they will deal maximum damage with a double strike (200%)...
Naturally, the overall morale bonus results in higher damage when a unit's morale is low, as the unit attacks twice, compared to relying on luck. Also, we consider the entire army, not each unit individually...
Read above, if you attack twice due to morale, you might get hit back, and sometimes quite hard, especially if you're fighting nasty griffins.
If I'm not playing as Necropolis or Conflux, I'll take Leadership because luck doesn't happen as often in battle as morale does... IMHO. The second turn can be used in various ways, but luck can't;)
Let's imagine a situation. The hero has one last inventory slot, and you are offered to choose between leadership or luck. What would you choose?