Just trying to find ground upon which to stand, especially for leftists and Jews, was a major challenge. Trying to formulate a way forward given the recent past and the fragmented post WW II political and social present was also challenging. That was, IMO, the 'existential' situation.

"It is not necessary to have hope in order to persevere."

I'm currently reading "The Fall of France" by Julian Jackson.
France had the largest, most modern, tank force in the world on paper.
Unfortunately, despite the orders being placed in early 1938 (at whihc point they were added to regimental numbers), French military mobilisation in the beginning of '39 massively depleted the skilled workforce needed to build the tanks just as the production lines were really beginning to work. Delays due to worker disruption, corruption and plain incompetence had prevented much production in 38. It was May before manufacture began again. Indeed, most of the new tanks were eventually re-deployed by the nazis, straight from the factory, on the Russian front.
You are right about flanking attacks. de Gaulle (yes him) led one such attack that knocked the german advance back. However, this was at the cost of nearly his entire company. If he had been succesfully reinforced at that point, it's quite likely that the advance could have been halted in its entirety.
Sadly, the lack of co-ordination by the French high command and their unwillingness to talk to the British except to lie to them about the forces available meant this was impossible.
At the beginning of the campaign Billotte had been tasked with the co-ordination role between the high command (who lived in a castle with only carrier pigeons for communication - no phones, no radio) and the entire French and British effort in N France. A classic case of the separation of authority and responibility. Bilotte apparently burst into tears because he knew he could not make it happen. It took him 4 days to pull a staff away from reluctant superiors.
When he was killed in a car crash, a British commander darkly suggested that his absence, even if not replaced, would only improve things.

keep to the Fen Causeway

You only have to look at all the countries around the world who welcomed the jews on the ship MS St Louis as they fled nazi Germany to gauge the levels of anti-semitism at the time.

So that would be EVERY country stuffed with anti-semites

keep to the Fen Causeway