In the show they said that the French army was considered one of the best in the world at that time or at least at the end of the First World War, what changed?

It's hard to comment on what people's opinions of the French Army may have been at the time, but France historically was considered one of the strongest land powers of Europe.

I also heard and read that early on the French had superior tank divisions, but lacked an air force that the was comparable to the Germans, any reasons for this?

I wouldn't say they had superior divisions, but it could be argued that their tanks were individually better than Germany's. The most common French tanks in 1940 were the medium Renault R35, the heavy Char B1, and the light Somua S35. Each of these tanks were generally better armed and armored than their comparable German tanks at the time. Most combat reports from the Battle of France describe French tanks as being at least equal to their German counterparts: https://en.wikipedia.org/wiki/Battle_of_Hannut

The problem is that French doctrine at the time required their tanks to be distributed among the infantry for support, whereas Germany tended to concentrate their armor into large formations for swift breakthroughs. From memory, I believe the French may have had only one or possibly two fully manned and equipped armored divisions by 1940, and attempted to raise a couple more during the Battle of France. The Germans on the other hand had about a dozen from the get go. So organizationally, the Germans practiced a more modern and superior doctrine which ultimately won the day.

but lacked an air force that the was comparable to the Germans, any reasons for this?

The French air force was actually comparable in size to the Luftwaffe. When supplemented by UK and Belgian planes, the Allied air force was actually larger than the Luftwaffe. Interestingly, the French suffered a chronic shortage of spare parts which meant that only around 30% of their planes were serviceable at any one time, which gave the Germans the de facto superiority in numbers.

One of the major reasons the Germans were so successful on the ground is that they could count on timely and accurate supporting fire from the air. During the Battle of France, German ground units could call for an air strike at any time and expect it to arrive within an hour, which was virtually unheard of in any armed force up to that point.