Maratha is not really overpowered. The economy of the Indian subcontinent was historically very rich and it wasn't until late 1800s (already a good century under British colonization and wealth being sucked out) that the economy of the subcontinent began lagging that of the United States. If you have the entire India under your rule and you have the military-strategic vision of the then hungry Europeans and Americans, you can basically make India a superpower.
What the game lacks perhaps, is it is missing an extra level of court intrigue/betrayals/factionalism etc which is really what allowed for the British to establish themselves in India (not technological advancement).

Historically the Marathas were all set to take control of the entire subcontinent in the mid 1700s, read the article on Third Battle of Panipat on wiki to find out what I mean.