Originally wanted to talk about both side, but I realized I would have to spend way more time, instead I will mainly focus on France.

The superiority of France, and the allies is above all economic and to a lesser extant a relative material one.

In 1939 France had the 3rd world biggest gold reserve 9.1% of the world reserve (UK had 12.9, US 54.4, Italy 0.8 Japan 0.6, and Germany even less!) and the allies have the control of the oceanic lines. Crucial resource such as oil, rubber, non-ferrous metals and even grain could only be imported in limited quantities for Germany. After 1939 its' main partner became the USSR through the economic cooperation agreement of the Molotov-Ribbentrop pact. But even this cooperation was limited, partly because without Gold, the technology or material Germany could give was limited. Between February 1940 and June 1941, the USSR only exported 900.000 tons of oil while Germany consume 5.8 millions of tons for the year 1940.

Meanwhile the allies could rely on their immense empire and the formidable industrial power of the US. In September 1938 France ordered from the US 1200 bombers and 700 fighters, before capitulation it ordered 4426 planes from the US (over twice the German production of 1939) but only 980 were delivered before June 1940.

France has an edge in numerous sectors especially artillery and motorization: It has 400 000 trucks against 120 000 for the Wehrmacht. It has 10 000 mortar gun of 60 or 80 mm against 6800 for Germany, 9300 canons of 70 and 105mm against 8600 for Germany and 600 piece of heavy artillery against 150 for Germany. The only artillery domain where France was outmatched was the number of anti air artillery pieces which were also way worse then their German counterparts.

The figures varies depending on the sources but they all point that Germany had about the same number of tank as France. Furthermore Germany could afford this was only because they seized the Czech tanks stockpile and mean of production. France has 2982 light tanks and 935 heavy ones (Somua, B1/B1bis, D2) in May 1940 as opposed to 3465 German tanks with 20% of Pz III and Pz IV and 7% of Czech Pz 38(t) with the rest also being light tanks. This figure does not count the British tanks from the BEF (around 600 half of which were engaged) nor the tanks from the Benelux. The German kept a tactical edge because of the systematic usage of radio allowing an excellent inter-arm cooperation and a better designed turret which allowed a gunner so that the chief of tank can instead observe the battlefield and command.

As for the air force, France has a small inferiority in number (about 3100 vs 3600 planes) compensated by the presence of the Royal Air Force. However the French had issue with designing modern plane engines for various reasons and even their best fighter model the Dewoitine 520 produced in small number was still inferior to the German BF-109. Even worse, France has massive organization issues, only 37% of its fighters built between November 1939 and May 1940 were deployed on the north-east frontline. There weren't enough mechanicians, electricians or even pilots. (roughly missing 33% of the required manpower). The previous problem also caused the French pilots to have an awful sortie rate and the French pilots effectively fought in an inferiority of 1vs3 against the Germans.

But what made the difference was the military doctrine and tactic

The French operational doctrine called the "Bataille méthodique" (methodical battle) was above all based on the 1918 experience of the French army.

Its' aim was to unbalance the enemy by a series of distributed attacks over a large front, supported by a mass of tanks to accompany the infantry and a motorized artillery. Such a battle would gradually suck up the enemy reserves which would allow to exploit the breaches until a general enemy retreat In the summer of 1918, the French made perfect use of their superior motorization to move infantrymen, artillery and tanks from one sector to another, making the transferring in a few days while that the Germans would take a week to move by rail.

The French generals have become masters in the art of conducting complex nested assaults chained in time and space, supported by hundreds of planes and tanks advancing under the cover of omnipresent artillery and became logistical master in order to fuel the prolonged attacks.

The drawback of such complex operation was that it let little place to improvisation and required lot of planning. The slowness of the France to react would become a deadly poison and the overcomplicated and hierarchical nature of communications did nothing to speed up the decision-making process:

Gamelin set up his headquarters in Vincennes, east of Paris. The second in the chain of command, General Georges, was based closer to the front, at La Ferté-sous-Jouarre. Under Georges depended Billotte, on whom depended army generals Blanchard, Corap, Giraud and Huntziger. The usage of radio was minimal in order to avoid the information being captured and decrypted and orders were transmitted by field telephone. Each information had to come from the very bottom, so that the upper scale take a decision and then the order has to be given and transmitted trough the overcrowded command chain. Such slowness was not compatible with modern warfare especially when the German generals did not hesitate to show local initiative.

In the meantime, France faced a sclerosis of the military theory and lost contact with reality. Under the guise of deepening the understanding of the battle, the French thinkers locked themselves in pseudo-scientific deadlock: referring to the War School, Beaufre felt that "he learned narrow-minded tactics, taking the form of the simplest action, and the appearance of an engineer's cost estimate." The thinkers established quota and scale of the required strength and pace required for attacking a X front over a width Y over a depth Z and in a time T. Those pseudo calculation did not fare well and had nothing to do with the friction of wars. When General Prételat demonstrated in 1938, during manoeuvres, that the Germans could emerge from the Ardennes in 60 hours, the upper generals told him to remain serene: it would then take the enemy a week to attack in force on the Meuse because it would take the French army that much time and because that's how they imagine war.

Finally, while the brain of the French army was defective, this was also the case, to a lesser extant of the arms. France. From 1928 to 1935 the military only lasted for a year and under a system of double incorporation. Meaning that each regiment took rookies every months, effectively preventing the army from having an operational division and execute complex manoeuvrers due to the high number of fresh soldiers. This was one of the reason the French couldn't contest the Rhineland occupation by Germany in 1936 (the other main one being the gross overestimation of the German army). The French also largely waste the 6 months of the Phony war and still lacked of training. Let's take the example of the 55th division of infantry. It was a reserve division composed of 30+ Y/O soldiers who had done they military service a decade ago and was placed at Sedan, a sector with the reputation of being calm. The officers tried to compensate its weakness by fortifications. Instead of training they instead largely acted as builders and built trenches with disastrous result, this division under enemy fire an tanks almost immediately collapsed.

Was everything wrong and terrible in the French army? Certainly not. At the strategical level, the allied shared the same vision of economic total war, relying on their superior industrial capacity while exhausting of the enemy potential under a blockade (to which they added a strategic bombing campaign). At the operational level, the emphasize of organization and logistic was kept as well as the idea of destroying the enemy through a combination of operations along a large front line. This is true finally, at the tactical level where fire takes precedence over manoeuvrer with intensive use of independent support battalions (half of the tanks were not endivisioned and cooperated with infantry divisions as well as two thirds of the artillery).

Simply put, the French Army was a fine tool which required its' rust to be removed and a few adjustment but France was defeated before this could happen. Once serviced by a total motorization, by the best of communication systems, the adoption a better inter-service integration/cooperation with the aviation, and more initiative and boldness were given to the local commanders, this doctrine worked perfectly fine, and this mature version was the one the Western allies used in 1944 and 1945.

Sources:

The Blitzkrieg Legend: The 1940 Campaign in the West by Karl-Heinz Frieser (1995)

The action of the air force in 1939-1940: structural and cyclical factors of a defeat Philippe Garraud (2001)

The role of the "defensive doctrine" in the defeat of 1940: too simple and a partial explanation Philippe Garraud (2004)

The war of 40: Understanding the defeat: The forest of the Ardennes Frédéric Guelton (2014)

The tragedy of 1940 André Beaufre (1965)