Wars are won by killing the enemy and breaking their stuff. By capturing and controlling land, means of production, supply and transport lines, and so on, you impose your will on your enemy and remove the capability for them to do the same to you.

Drones will be used to destroy enemy assets, take out ground troops, and maintain control of of the above mentioned resources. You’ll never just have one drone army meet another on an open field, that’s not even how human soldiers fight anymore.