But it's easy to over generalize what he's saying.
It's absolutely best practice for modern infantry to improve their defensive posture while staying in place. You can see this by the extensive trench system both sides of the Ukraine war have constructed whenever positions get fixed for even a relatively short period of time.
What is often forgotten about the Maginot Line is that... it worked, it did exactly what it was supposed to. The failure was in French military leadership, largely for reasons that probably would have played out the same without the Maginot Line (e.g., refusal to believe intelligence reports, slowness in response, etc.).
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.
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 France.
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 wasn't a game ender for WW2. But could it still be useful now to supplement a modern approach?
Nowadays it's still used as a French expression to describe a "seemingly impassable defense that's useless in the end".
https://en.wikipedia.org/wiki/Battle_of_France#Central_front
Quick summary: The French Army's high command was stuporhumanly slow and weak in their response to the German attack through the Ardennes (just north of the north end of the Maginot line). Especially considering how quickly the German Army had conquered Poland less than a year earlier. And had conquered Denmark just one month before. And was wrapping up the conquest of Norway at the same time as they started attacking France...
If you know in advance that your soldiers are solid (and the French soldiers were) but your military high command will be worse than useless - then relying on fixed fortifications is actually the best possible national strategy. Your good soldiers can hold out for a while in the fortifications, taking (mostly) not-too-horrible casualties, without needing any orders from or action by your brain-dead high command.
For Lord Gort - it wasn't his country, he'd only been appointed to command the B.E.F. the prior September, and he'd been shuffled through a lot of different jobs in the prior decade. (Including time spent in China and India - hardly useful experience for WWII in Europe.) Still, Gort and his immediate subordinates got their sh*t together, moved fast and made good decisions in very new, chaotic, and challenging circumstances, and did extremely well.
For Gamelin & Co. - it was their country, defending it against a German invasion had been their d*mn-obvious Job # 1 since at least the German invasion of the Rhineland (March 1936), and they'd been building the Maginot line since 1930. Yet their performance in the event was laughably slow and weak even by the 1914 standards of French General Joseph Gallieni. (Who had been recalled from retirement, was in obvious poor health, and had served most of his career in French overseas colonies.)
The naive analysis just looks at the military effectiveness of the options. But there may be political implications. Perhaps if country B spends the money on tanks, that gets noticed in country A. That changes the politics in country A and lets the Fighters there persuade their own Peace-niks that more "defense" spending is needed. Whoops! The money that country B spends on tanks doesn't help defend country B as much as you would expect, if in unleashes counter-spending in country A.
What about country B spending the money on static defenses? That could help Peace-niks in country A push for cuts in country A's "defense" spending. That would multiply the effectiveness of country B's spending on static defenses.
I don't think it worked like that with the Maginot Line. Nevertheless, what a General says about military effectiveness misses part of the story.