But there's a difference between loss of life in combat versus deliberate murder of noncombatants outside of a combat situation or of prisoners who are in your care. It's not about who has the highest scorecard of death and depravity.
Ask the same question about incendiary bombing, which happened throughout the war. The B-29s dropping incendiaries on Tokyo killed more people than the atomic attacks. Are those pilots war criminals? Are the artillerymen who leveled towns and villages full of people war criminals? Based on the "total war" approach embraced in WW2, they were not.