In my honest opinion, the computer doesn't make enough cavalry for chariots to be worth the time and trouble. If you look at the civs that do get chariots, they are surrounded by civs that only use HA and chariot archers, so the anti-cavalry ability is sort of null and void. Against infantry, the brits are right by germany (spear warband), Seleucids right by Pontus (pikemen)/Egypt (nile spearmen), Pontus by Seleucids (pikes)/greeks (hoplites)/egypt (nile spearmen), etc.

The description for scythed chariots states that they are heavily armored, but they have a defense score of one? The dude in the chariot is dressed up like a cataphract unit, but he might as well be naked to represent his armor status. If the Chariot was armored a bit more, I could see a bit of use for them in SP.

MP, on the other hand, is anybody's guess. I know how fragile MP is to slight changes, being an AoE 3 veteran.