This is a fairly decent critique of the Avenger’s Endgame final battle.
We all know it had flaws and one of the biggest ones was that we were never that worried about the heroes once the battle was underway.
The key to a decent battle scene is that it needs to be treated like a mini-story. Remember, no audience wants to read about a realistic military operation. They don’t want to be educated. They want to be entertained.