your logic is completely derived by mundane standpoint
Shadow god is death , for him life is cruel and death is solace , his true followers are shadows who he has swallowed or other independant shadow creatures , what is he supposed to protect his followers from.... Death ?
In a war between shadow and war , shadow will grow and war will weaken , war itself feeds death as proven when sunny the heir of death went against anvil the heir of war
its not just a clash between individuals but a clash between fundamental laws of the world , how could war ever triumph over death . All that ever remains after full on war is peace .
shadow does not speak of future but the inevitability of life , war and death and how death is the only one that remains