Correct. They don't have to be perfectly balanced. Some people like history so they will want to play certain Civs or try them all. Some people are powergamers and will only want to play the most powerful Civ. Some people will only want to play their native country. There will be Civs to suit each play style.
I think that's perfectly reasonable as long as one Civ isn't ridiculously overpowered. Even then, in single player it doesn't matter and in multi player people can ban that Civ if they choose.
As said earlier, I think the best solution for all would be to have some sort of option that you choose before starting a game, like "Balanced civs" vs "Historical power"