Pretty simple suggestion but rotate the hero challenge based on class so every class has the opportunity to get different hero skins and hero charms.
#Rotate hero challenges based on class
silver radish
foggy plover
Originally, this was how it rotated about, more recently there has a been a bit of imbalance but I'd say this is definitely something I both agree with and suspect the devs do have in mind already
silver radish
I figured as much, and I understand the impetuous of having certain heros in the rotation based on events