Majority of endgame battle I played are choatic. Like in a very Huge map in Dominion 3, age of wonder games, and many other similar games that you have to controll muitiple individual units pieces on the map.

Give heros general skills rating, so that they can act like another AI player but you have control on what he will do.

This will lessen the amount of micromangement in the game. And let you focus on the main plan to defeat your enemy

Your hero that act like general and will act like allies in tatical battles or aid in reinforcement.