It's not just chariots that are broken, their counters are as well.
TL;DW:
Elite Heavy Barbarian Spears can't stop chariots.
Levy/Militia Medium Hoplites can stop chariots.
Barbarian Shield Screens can only stop chariots reliably if they are deployed by Very Heavy units, while even Medium Hellenic spears can stop chariots frontally with Hoplite Wall.
The Hellenics also have another tool - very heavy shock cavalry and the tiers above. The Barbarians, aside from the Getae lack this, and the result is that chariots are almost impossible to counter with many barbarian factions . Oh, and arrow fire seems to miss more than it should as well.
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