The Maginot line in France has become synonymous with a useless measure of defence providing a false sense of security though.
It's a combination of several things.
First military hardware is a lot more expensive. A ww2 tank was a big piece of iron with a diesel engine in it, a modern tank has a ton more tech, all produced in small series (imagine the cost of the iphone if only 1000 were manufactured a year). That's even worst for planes. You can't line up an army on the scale of ww2 armies. And since the EU can't agree on single plane or tank design anyway, the volumes for each device are tiny and design/fixed costs hugely expensive to amortise.
Then you have socialist or quasi-socialist governments all over Europe, in France in particular, but even in the UK, slashing military budgets to launch big redistribution programs, along with building up big bureaucracies since the 80s. Government spending managed to go up as the share of military spending and other basic services (police, justice) went down. The problem with benefits is that people come to rely on them and then it becomes politically impossible to cut them back (same thing in the US), unless you have a Thatcher, but there is none on the horizon. So basically now these countries are stuck and have zero wriggle room even to face imminent danger.
That's the cost of free riding on US military spending for half a century. If an elected Trump walks away from both Ukraine and NATO, Putin will have free reign to bully the other missing pieces of his russian empire (moldavia, baltic states, even poland). And there will be little a country like France will be able to do with its small military samples. Its army was seized to bomb terrorist camps in Africa and nuke an invader. They have nothing in between.