Native Warriors are stronger than normal units, most of the time, so the Wood costs are justifiable.
A Native deck with the cards, can make them 2 or 3 more effective that regular units, even with the expensive Imperial upgrades (while Natives are cheaper to upgrade, and the Legendary upgrade affects them all at once).
You also have to account that they are not only strong, but have no population cost, which means they should absolutely be expensive and limited in number.
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