how was spitz a poorly developed character?

Spitz was poorly developed because he only had one side to his personality. He was the leader, but he was tyrannical and greedy. He took Buck's place in the snow, and the only way he was "going down" was through death.

Spitz is a secondary character. He is the last rung of the ladder that Buck needs to climb (displace) on his journey to become leader of the pack. It is important to keep Spitz poorly developed because we aren't supposed to like him. We aren't supposed to feel sympathy at his fall, but rather feel exhilaration at Buck's accomplishment.