That line actually worked fine. But it was not extended along the border with Belgium for political reasons. And the Belgians and British were to hold the line in the North. Of course that failed.
It was a new kind of war that the British and French could not imagine.
But France learned the lesson from that. They went solo from NATO, and do not depend on NATO to defend them. They went solo with their nuclear arm as well. Unlike many other nations such as the UK which essentially integrated their nukes with ours.
the French were part of SEATO instead..
South East Asia Treaty Organization
The US, Australia, New Zealand, France and was it India or Taiwan ???