You're not taking into account several factors. First of all, If you're looking to warmonger then you'll need to improve some luxuries to insure you don't dip to far into unhappiness, meaning you probably won't be going straight for the chariots. Second of all they're easily combated by spearman, and in this case being in flat terrain won't help you for a couple reasons. Since you can't move after attacking, and since they only have two range, then in flat terrain this means spearman will instantly be able to reach you from the city you're attacking. If you're in rough terrain the reason you built them in the first place, early rushes, will be useless as you will lose all mobility. Finally, its much harder to war before around T80, as without siege weapons it'll take many more units to bring down a city. This means that if your opponent has any military at all, it'll probably be a losing battle.
Overall, mediocre unit, better to wait that extra 30 turns to start warring, as you'll be more developed then. If it could just move after attacking, then that would tip it over the edge into a higher tier unit, but as it is it stands easily defeated.