The Weygand Line I am referring to is the line established by Maxime Weygand in the aftermath of the hugely successful Fall Gelb. Immediately after the evacuation of Dunkirk, French soldiers were being repatriated back to France and presumably bringing back with them knowledge and expertise on the German's tactics. French military technology was also on a parity with the Germans, with better tanks (such as the Somua S.35) and artillery. Their lines were also anchored on the rivers Somme and Aisne. The advantages the Germans had was the number of divisions (142 vs Weygand's ~60) and the qualitative superiority of the Luftwaffe. Significant advantages, yet, it only took 3 weeks for the French army to utterly collapse.
How did the French army collapse so quickly? Were the German advantages in numbers and air superiority that decisive?