Just looking from a German point of view. Germany is struggling to bring down 3 and sometimes 4 major powers (France,England,Russia,Italy). The Entente has Germany,and to a lesser degree AH.
If we change the rule, Germany would need a major victory against all four (4 seperate battles) to get the same result. Whereas the entente can hammer Germany with a loss from each and every country.Germany needs 4 victories,to the other countries single victory. I feel this could be unbalancing.