I read a book about the German attack on the Maginot line in June, 1940 (from the German perspective). Both morale and performance were poor.
Indeed, the overwealming French superiority in the Saar offensive produced no meaningful results, although as you propose, that might have been more the result of poor leadership than performance by the troops.
The French had an entirely defensive mindset in 1939-40, the total inverse of 1914. Even when presented with the opportunity to attack the lightly defended western defenses of Germany in September, 1939 they couldn't bring themselves to do it.