Why putting in a unit at all? Or at least, another chariot?
I think all what T'C-S&A needs is a cheap castle, so you can build those chariots everywhere ... and you don't need at mod for that. Do you really need more than 4..8 chariots in one army?
What the theme is lacking are support troops for the chariots .. riders or infantry that can keep up with them and prevent them from being ganged upon.
But thinking about it, wasn't that a very common historical problem with chariots, especially those which where designed to "trampled" into enemy ranks?
And adding a lance/spear to them makes things even worse - what IS lacking from the chariot commanders is the ability to repell attacks. You have to put at least a stinger in their hands for that, but with your mod one get everything -not for free, but at a discount price :
- the ability to repel
- (some) safety from being closed in
- front line of trampling, highly-armored troops with high tactical and strategical mobility
I found that the chariots do quite well if decked out with low-level fire resistance gear. Drive them right through the friendly fire of the Demons of Heavenly Fire, right over the remaining enemies. Nothing much left what may route afterwards
Reminds me of some test the British did in North Africa: Driving the Cruiser (?) Tank through 3" arty fire (HE). They found it worked quite well - the arty did a great job in surpressing enemy infantry, but worst what could happen to a tank was immmobilization.
A.