Indeed, Battle of France was harder won than commonly tought : infrastructure, logistics, etc. It was the first invasion of a country that could have inflicted defeat.
Now, if in these two years, some french generals died, the younger generation manage to impose theirs ideas, it would be even more difficult : after all the french tanks and british planes were superior to the german ones in many occasions, but their use was linked to a bad tactic.
Makes Gamelin quitting the scene for some reasons (and you would maybe butterfly Waygand because of age limits, it would help to have a general that doesn't plan to attack USSR and Bakou during the war with Germany) and it's done.
For the Balkans, the time plays in Hitler's side. The situation can evolve in even worse parts, and maybe the states as Yugoslavia could pass on Axis' side "paecefully", critically if Mussolini is not acting stupidly.
For Eastern Front...Attacking later is a certain defeat : Soviet army would be even more bigger, with a better material (the better tanks were still in production during 41), and as the Soviet leaders and generals waited Hitler's attack in 42 or after (it's the problem they had with Barbarossa in 41)...