Wasn't WWII a lot like WWI under all these categories IOTL?
1) The Siege of Leningrad and the Italian Front, to say nothing of the war in Belarus certainly all qualify for this. Not to mention the Battles of Narva. Much of the actual combat and the way victories were won boiled down to attrition. Certainly the Soviet victory qualified as that, and the victory of the Allies in the West has shades of it. Can we really say that the Bocage fighting wasn't attrition? Or God forbid the Huertgen Forest?
2) WWII was plenty grey IOTL if we look at it. Obviously the Nazis are in nobody else's league, but they don't have very many pre-modern equivalents either. Maybe Genghis Khan and Tamerlane but that's about it. You had the British do things like this:
http://www.oldindianphotos.in/2009/12/bengal-famine-of-1943-part-1.html.
You had the USA and British both accept area bombing, which in the words of people like Bomber Harris was purely "let's kill enough civilians until morale cracks. You also had not to mention Mao Zedong as a leader of one of the major Allied movements (albeit after 1942 Japan rendered him irrelevant in the not-very-subtly named Kill All, Burn All, Loot All offensive). And of course the Soviets pulled off things like the Katyn Massacre and got Nazis hung for that one. It was very much black and grey, and the guys coming across the *least* nasty of them all are the USA with its concentration camps for Japanese, Italians, and (some pro-Nazi) Germans, its strategic bombing campaign, and its atrocities, primarily in the Pacific Theater.
By comparison both the British and the Soviets had mass-scale atrocities as their responsibilities in this timeframe.
3) The Cold War and decolonization certainly showed a great disenchantment with the pre-WWII Great Power establishment......