It holds up if you assume war crimes are beneficial to your goals but there is quite a lot of evidence, and sophisticated theory going back to clausewitz, that they mostly aren't.

They can look useful at a certain level of conflict, but once you are thinking of war as being a tool for accomplishing policy goals (how modern nationstates view it), a lot of the things you would "want" to do stop being useful.

Wars that can be won quickly through decisive military action alone are quite rare historically! More often things like support/enmity of the local population, political will in the home state, support for recruiting or tolerance of conscription, influence of returning (whole, dead, injured, all) veterans on the social structure all become more decisive factors the longer a conflict runs.