Just because political concerns ruin your tactic, doesn't mean those political concerns aren't real. The Maginot line was great tactically, but worse than useless strategically, because it completely failed to achieve it's big-picture objective - keeping the Germans out of Germany.
Either way it's a moot point. As I said, the Ardennes would have been an effective barrier if it was better defended. You can't leave an unguarded opening in your fence and then declare that fences are useless.
Yes, France still fell in the end. Static defenses weren't able to overcome weak leadership, but - importantly - it's mobile forces weren't able to overcome it either. In the end the mobile forces ended up being _much_ more susceptible to poor leadership than the static defenses, leading to a large chunk of the army getting disastrously cut off (and the need to get evacuated from Dunkirk).
For a little bit, anyway. But what does that actually mean? I often wonder what would have happened had Germany not pursued genocide, and just stopped at France. It's not like the French people would magically turn German overnight. Would the resulting entity end up like a confederacy?
Same reasoning with Napoleon, too. What if they had stopped before the Russia disaster?
Though I wonder if Hitler could have made things worth if he had not started the Eastern front. (I'm not clear on how that started, and Stalin wasn't to be trusted)
It's kind of like building a giant fence around an area, then leaving an opening in the middle of it, and then deciding that you don't need to have people guard that opening. And when people inevitably get through the large unguarded opening, you declare that fences are idiotic and useless.