Gruumsh as a god of fury, destruction, and battle works. He represents the chaos, destruction, and unpredictability that exists in battle as well as the fury and adrenaline that pushes soldiers of all peoples forward. Yes, there is slaughter too, but battle is rarely pretty or won without bloodshed, particularly the bloodshed of infantry. Generals and nobles may offer prayers to gods of strategy and conquest, but the rank and file soldiers of the world who bleed and have battle scars call upon Gruumsh. Gruumsh One-Eyed was injured on the frontlines of combat and therefore knows pain of the soldier unlike the war gods of the backline or who bark orders from the safety of their camps. To be a god of bloodshed is not only to celebrate the blood shed by foes but also the blood shed by you and your allies to win victory.
Would that make Maglubiyet, Corellon, and Bane the war gods of the backline?
Frontline: warriors
Gruumsh
Bahamut
Tiamat
Moradin
Backline: commanders, warmages, and archers
Maglubiyet
Corellon
Bane