Not so many people are playing inca, but everytime i play against one, its to over powered overpop and so strong eco why ? Dont get it they need a nerf and always running running running …
i really like to play inca. they are a bit strange in the beginning and you definitely need some time to understand some of their cards. Chimus and Chasquis allow really unorthodox gameplay aswell.
i think they are atm to unorthodox for most players and the community needs some more time to discover the full potetial of incas. this lack of knowledge maybe also the reason for their success.
I’m no high lvl player, so i cant tell you, if they are actually overpowered, but i can tell you: fighting against heavy cav or lancers does not make fun at all and long range artillery - in a well defended position - kills like half your army 
To defeat the Inca, I recommend massing musk cannon, once you can get a significant mass of musks and like 4 falcs, it’s very hard for Inca to win unless they use the stronghold