As Epeiros (see faction progression post) I waded through a sea of Captains who had nothing but Triarii and Pedites Extraordinarii. It's an epidemic. Their fullstacks, however, I find to be more balanced. Of course, my Hellenistic phalanx and HC augmented with Thracian and Celtic auxiliares (Cordinau Orca, to name one) utterly mauled them. However, I can easily see Celtic factions having trouble with an armies like those.

By the time they got Polybian reforms, I had taken all their settlements in Italia except Arpi. Again, see AI faction progression post.