I would really love it if this game did not allow duplicates. That they were all part of the city you create and that way it would not make sense to have two identical heroes. It would also make the benefit of not allowing summons to be duplicates of what you already have - that way, when you have summoned all three stars, four stars, standard five stars (yes, spent a whole lot of money!), it would be easier to get the heores that you really want.
Today it is really the opposite - if you have spent a whole lot of money to get many heroes the chance of getting a hero you want is really slim and you end up with endless duplicates that will never be leveled. And let’s face it, hero academy didn’t really solve the issue…