Hello! I think I might have the solution that has kept us going in circles for years. Here is what it is. Firstly instead of making infantry with names of their battalion or unit I think giving them classes should work better. And no, these are not upgrades to each other.
These guys are more heavily armed than regular infantry
These are the ones that charge up the field, I think they should have the ability to heal and have more health than medium infantry. Just not the fire power
They are fast and should have a hide ability
These are sappers, minesweepers and engineers. Basically they are jobs that are specific.