You’re mixing up your argument. Are you using the Serbian argument that the invasion of Yugoslavia stalled Barbarossa by a key few weeks or are you using the communist argument that Tito tied down 36 divisions during 41-44?
I am not "mixing up" anything, Dio. You are trying to drag a red herring into this argument by turning events into a set of ethnic and political "views", and therefore up for grabs by anyone.
Ask military historians which arguments ("communist" or "Serbian") that they are using to come up with the reasons for Barbarossa's failure?. And the answer would be "neither". Because they all agree that Serb & Greek resistance helped delay Operation Barbarossa which ultimately resulted in its collapse and lost Hitler the war. The only disagreement between them seems to be whether or not it was just "an important factor" or "the totally decisive one" -- much to your chagrin, I am sure.