Bombardment & Ground Combat should happen after space battles in a separate window.
Are there really any advantages in doing this inside the combat mode, rather than after?
Are there really any advantages in doing this after
combat, rather than during? You haven't listed any.
But yes, the point is to increase the role of maneuver, and choice of strategic goals in combat, not just have a battle of attrition. A player needs to guard his planets, as well as shoot ships, otherwise he may find that he's lost a planet, even though he won the space battle.