When a chariot archer is killed, then it becomes anormal chariot and tries to trample the opponents, doesn't it? At least that is what the description makes it sound like. If that is the case they could be used defensively. Give them a command to just fire, then should infanrtry approach and kill an archer,t he chariot will then trample the attackers. It could be worth experimenting with.
But to make it worth the cost the chariot should have two archers in it.
I think chariot archers on "hold and attack" will first stay put firing a bit and then charge the enemy for some trample action. If so, they are not useless at all.
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