Although Heroes may look the same, but they differ in their Parameter Trends.
When looking at the Base Values within the MCH Reference guide, you may see variations or changes in parameters to a certain degree.
Heroes of the same level will pretty much have all the same parameters.
When you first do "Art Edit", the Parameter Trends will become randomized
Also, Heroes within your Inventory can have their Parameter Trends randomly modified from their details screen. You can do this as many times as you'd like, but it will cost Hero CE to do so.