They applied many tactics, and they did face the Romans and Celts head on in the open, Cimbri for example, treatening Rome and defeating them many times.
You seem to mistake them for the Lusotannan who's main tactic is ambush.
You talked about him putting Hellenes at disadvantage, he's a Hellene himself so knows very well what he's doing. He also was playing as a Roman in the last tourney.
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