Re the OP- we're talking about the "Phoney War" correct?
Basically, instead of leafletting the german Army, if the British and French were "ready" and willing to take it to the Germans from the git-go- you'd need a lot more military spending, forethought, and practice that the
Brits and French didn't do OTL.
I think you're on target with with French demographics and war fatigue considering something like 20% of their men 18-35 got killed or wounded in WWI contributing to their defensive mindset.
Keep in mind the bitterly divided French politics between the Popular Front and conservative blocs that made everything a $%^& rugby scrum.
Once the Maginot Line was completed, they felt safe to keep bickering.
If history repeated itself, the French'd mobilize, the British would show up, and stop the Boche from being within Bertha range of bombarding Paris.
Could De Gaulle and other French officers developed a more dynamic approach to mobile warfare?
Yes, but the French military wanted to refight WWI with modern weaponry.
Losing their own campaign against internal resistance to changing doctrine b/c you had dinosaurs like Marshals Foch and Petain still calling the shots was what doomed the French military to defeat.
The French got a clue pretty quick when the attack came and cost the Germans dearly but it was too late.
Could the French have gotten it funded and from 1933-1938 w/o ASB's forcing the Third Republic to shut up and focus? I say, really unlikely.
Still, an unambiguous French bitch-slap of the Germans in 1936 over the Rhineland would have convinced them to fold, no blitzkrieg tactics necessary.
The Brits had other problems. For one thing, the British Army always got short shrift as far as R&D and funding priority and had its hands full with colonial ops that had little to do with conventional warfare.
Second, as many have commented on how the RN, FAA, and RAF were bitterly at odds in 1930's over doctrine, funding priorities, and hardly in the mood to develop effective combined-arms operations.
BH Liddell-Hart had some ideas on how to do that. Rommel and Guderian tweaked his concepts into their doctrine, but he was just a British Army officer so what did he know, as far as the MoD was concerned?
The Germans focused on nothing else but kicking France's ass and they knew they had to do it quick before they could fully mobilize. From 1920 on, they made it their mission to develop their skills at maneuver warfare and combined-arms ops so they could create and exploit weakness in the enemy's defenses.
They had free rein in the USSR from 1920-1933 to learn how to manuever in open and wooded terrain, then got a chance to demonstrate it in the Spanish Civil War.
The Soviets took notes and developed their own flavor- Deep Battle from Timoshenko, among others.