If I had to choose between dug out fortifications that Germans know nothing about or concrete boxes that were scouted way ahead of time with every gun emplacement known to the enemy I would choose dirt. In Lithuania Russians build massive fortress around Kaunas. It was mostly finished for WWI, even today it looks pretty impressive. Germans pounded it to bits in one week. They simply brought railroad guns and pounded defenders unable to answer... According to Wiki Germans attacked Maginot line in something like 5 places and were repelled only in one.
Besides, Germans were doing heavy recon of the border, they'd have had eyes on the MLR from the east at ground level and air. They'd have known exactly where a crappy hasty built defensive position was located and when they find it that's then the local schwerpunkt/main effort attack, at least if its the option of hasty vs fixed heavily built fortifications.
And when indirect arty and direct fire field guns are shooting, you'd be a fool to want the protection of a few sandbags or logs versus numerous feet of reinforced concrete (meaning steel rebar) and hardened steel cupolas and gun ports.
I get why you're arguing this. Because you read online or very generalized and inaccurate accounts of WW2 that the Maginot Line or maybe you read Patton's stupid quote about fixed fortifications. But then you skipped how all the worst casualty producing battles in the war by attacking forces occurred in either severely constricted terrain favoring defenders (urban, bocage, mountains), or else against fixed fortifications properly constructed, manned, and defended.
The Maginot Line's only real fault was its continuous forts ended about 25 km short of Sedan (which was why that was the schwerpunkt for the entire German attack).