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.
What "resistance"? The Yugoslav Army didn't put up a fight and signed an armistice on the 17th of April. Are you referring to the German drive into the Balkans as delaying Barbarossa? A delay? Certainly...and a costly one. But this "resistance" that you speak of (if you're referring to the Chetniks and/or Partisans) had no effect on Barbarossa since all the important units were already driving into Russia and the Germans left only a skeletal force in the Balkans.