I don’t think the Allies would automatically win if France wasn’t eliminated on the first round. Russia will probably start out pretty weak and won’t threaten Germany for a few turns. Plus there shouldn’t be many units in the UK to cause Germany any problems.
I don’t want France to be a complete walkover for the entire game. I’d like it of they at least took a part in some African battles, as they did in the actual war, and I want them to have a respectable navy. I think the best rule would be one similar to China’s: were, even if they loose their capital, they can still collect IPCs and build infantry and artillery in their African colonies