As I understand it, Germany did not expect Britain to attack Germany directly in 1939 nor did Poland. All of Europe expecting the aid of the Allies to come in the force of the French Army, with the Royal Air Force providing the only British support on the continent.
If this is the case, which it so obviously is, France should have been driving force and wedge into the German defences on the West Wall. And the RAF would be the supporting arm of the force, not any kind of striking component.
The British Army was ill-equipped, and was severely understrength compared to the other great super-powers of the world. Other than small arms, the French Army was generally better equipped than the British. However, the British power came from it's mobilisation. They did need more powerful and faster armour though. The reason the French should have been the driving force was because they were the largest army in Europe, and they were the greatest threat to Germany. Britain had to ship it's forces across the Channel - in 1939 this would be too late. It would be right to assume that Britain would have supported with the RAF only.
The French political situation was a great reason in their failure. They were underequipped because of misorders and under-orders of new equipment. But most importantly, in both France and Britain was not technical equipment but tactical thinking. Both should have been aggressive, and both should have used their mobile armour more like the Germans. This idea wasn't new to either of them, in fact it was the British and French that laid the foundations for the modern tank warfare which Germany perfected in World War II.
The Luftwaffe was out-numbered when over France during Fall Gelb. They sent 2,000 planes to Poland during Fall Weiss. Had France attacked, the Luftwaffe would have been overwhelmed. And the Heeres could not withdraw so easily to the West Wall, they would have to disengage from the Polish forces leaving potential pockets and encirclements open.
The French did 'attack' Germany in the wars only French offensive into the Saarland. The Germans didn't do anything as a reaction because they didn't want to provoke the French into a greater assault.
As for the West Wall:
"I soon realized what a gamble the Polish campaign had been, and the grave risks which were run by our High Command. The second-class troops holding the Wall were badly equipped and inadequately trained, and the defenses were far from being the impregnable fortifications pictured by our propaganda. Concrete protection of more than three feet was rare, and as a whole the positions were by no means proof against heavy caliber shelling. Few of the strongpoints were sited to fire in enfilade and most of them could have been shot to pieces by direct fire, without the slightest risk to the attackers. The West Wall had been built in such a hurry that many of the positions were sited on forward slopes. The antitank obstacles were of trivial significance, and the more I looked at the defenses the less I could understand the completely passive attitude of the French."
- Maj.Gen.F.W.Von Mellenthin.