The Indians have only one viable unit they can go for in the Castle Age right now : Camels. They also lost Arbalesters. This makes them a very boring civ, and also extremely predictable.
Also, The Indians are supposed to use Gunpowder to protect their camels, but they hardly use any until very late Imperial.
The idea is to solve these two problems by linking them to one single small change.
So, in order to make this happen in a controlled way, we can allow the Indians to have Hand Cannoneers from the Castle Age, hence, we would see Camels + HC play more often and it won’t be overpowered either, because both these units are gold heavy.
Also, Shatagni would come into gameplay use in more often early Imperial rather than super late game.
In Castle Age, Indians have a lot of viable units. Camels are the best option, but you also have full Castle Age Archery Range and Barracks rosters.
You can go for Crossbows, Cav Archers, Skirmishers, Pikes and Camels.
Cav Archer + Camel is a brutal combo for Indian Castle Age. You can still use your perfectly normal Crossbows, Pikes and Skirms, as they are baseline units, and counter whatever you need them to.
Indians are also a Boom civ, so by late Castle, you should be able to spam a lot of troops, and just overwhelm your opponent.
The only unit they miss in Castle, is the Knight, and they do not need it anyway, since their Camels slaughter enemy Knights, and going Cav Archer is always good as Indians, as you get FU HCAs in Imperial.
i swear you want change for the sake of change.
Indians are already a very strong civilization and don’t need any buffs.
they get cheap vills and the ability to boom with the best of them.
they get fully upgraded hand cannons with extra range, they get fully upgraded HCA.
they have solid siege
they have hussars on top of their camels, fully upgraded skirms, and halbs only missing the final upgrade.
and ofcourse they don’t use gunpowder until late imp. this is true of everyone except turks and spanish for obvious reasons.
you say they wouldn’t be op because both units cost gold, but ignore that they gather gold faster then pretty much everyone.
the fact you think indians having HC in castle wouldn’t be OP tells me just how out of touch you are.