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Leadership - runic harmony should be prioritized.
In defense - a fight to the last is essential (in my opinion, this is the main skill that dwarves should take).
Helmar, as it seems to me, is not the best option, but I might be wrong.
Simply, Helmar's advantage lies in the fact that he will cast the "Punishing Strike" spell slightly earlier (because even without that, after casting "Stone Skin," he won't move too far on the spellcasting scale).
Then, what should be taken instead?