You are talking like the game starts at late game. It is true that Hindustanis are strong in late game but before they can switch from camels/ghulam into HC, you have time to beat them (its super expansive to research infantry techs + chemistry + range techs + imperial castle tech for HC).
Do not forget that they have only camels and hussard in the stable (very weak vs almost everything, any infantry and even archers).
There major eco bonus is the cheaper villagers. So earlier you attack less this bonus is significant. To be honnest I do think Hindoustanis are OP. Ghulam has already been nerfed with le last DLC and the lost hallebardiers.