That's true. What I miss is more an analysis of the available resources, how these resources have been applied and what kind of equipment was produced and how. From a purely technical perpective one could argue that German tank development, as one example, was not perfectly geared for mass production under war conditions. Some of the welds on genuine WW2 Panthers were better then some you see on 21st century cars. Why would you do that during WW2? Also the maintenance and repair operations of the warring nations in WW2 deserve a much closer look, the framework to be applied is available now, albeit in the engineering domain and not the historical faculties.
And resources cover a lot more than just man power., So I would argue that the Allies in both world wars had more resources and industrial capacities and have been more effcient in applying them to the war effort. Obviously tactics play into that as well, as does operations and strategy. When you have more you can afford to burn precious power on risky or unsuccessful operations, when you don't you have to be more cautious in selcting your war goals.
Regarding slave labour. That was one way to offset the manpower used for combat. I won't go too deeply into the moral and social aspects of it here, let's just say that this was among the worst things the Germans did in WW2. Again what would be interessting is an analysis of whether it was worth it or not. See, I would assume that using slave labour would result in a much higher degree of rework for the stuff slaves produced. We are talking about Germans here, there have to be at least some numbers out there regarding this. Again, engineering knowledge can help to make sense of these numbers. And I could go on, which was the main reason why I decided to study history (even if it doesn't look like it will lead to anything right now, who would have thought that you can only miss so many lectures to be allowed to take the exam?).