I was thinking about solutions to the min/max problem. And I’d like to give a shout out to the abuser with the 10* Bronze Panzer for my idea.
What about implementing a system of gates that limit your hero development? For example a Bronze hero can only support up to 3* of development. In order to unlock Silver, all skills will need to be maxed. Then Silver will only support say up to 5* of development. Moving on to Gold will require fully developed Bronze and Silver skills. The can be further tuned at Bronze1, Silver1, Silver2, etc.
I would further put level caps by color development. You want to stay green? Sure. Enjoy a max level of 10. Bronze? Level 20, etc. This creates an artificial bracket system that severly limits the range a min/maxer can exploit.
Also, hero’s that start at 3*, 5* and 7* essentially still have those additional stars of development, but they are just locked out until the level and skill development catches up to their star rating. I would still allow people to add frags to any unlocked heroes, but again, the upper levels of those abilities would still need to be unlocked.