Which skills are best for a hero?

Right now, I'm experimenting with leadership skills for Necromancers. I took a hero – Lucretia, the vampire princess. Oh... and I'm struggling. She initially has Sorcery, and I also gave her Leadership. The hero isn't really appealing to me anymore. I've gathered a decent army. I took the Diplomacy skill. I started attacking neutral creatures. I've already attacked 8 groups of neutral creatures, levels 1-4. But no one has wanted to join me yet, even though the danger level was "low" and they are defeated without any losses. In general, I'm coming to the conclusion that leadership isn't necessary for a Necromancer. The probability of a neutral creature joining is too low. Maybe it will improve as my army grows. I'll see – I've only just started playing on this map.