Originally Posted by Sam-Nary
As the actual course of history shows... but the failure of the Schlieffen Plan has more to do with the Germans attempting to do too much rather then the French having better infantry. Remember, in 1914 the French army still wore bright red and blue uniforms that got them their single bloodiest days when they were gunned down attempted to retake Alsace and Lorraine from Germany... German casualties in those engagements, minimal.
As were the French casualties when the Germans just after the above event took to the offensive against the French fortified sector around Toul and Verdun. Holding it against any number of Germans attackers was simple enough to allow Joffre to pull an entire French army from that part of the front and fling it west of Paris.
You're not looking at effects of infantry quality, but of the WWI advantages of defensive positions against an attackers, which in 1914 worked pretty much the same for either side.
The French main problems in 1914 was in lack of long range heavy artillery, not infantry quality, and the Germans after all setting the pace of the action by the move through Belgium, coupled with the Germans calling up their reserves from day one and so achieving a massive numerical superiority in that area of the frontline.
Probably a better gauge of the quality of the French infantry in 1914 is that while outnumbered and outgunned initially, it still managed and orderly retreat — which is generally regarded as one of the hardest moves you can attempt — until such time as they could successfully counterattack the Germans. That's an actual sign of quality. The colour of their pants in an incidental detail by comparison (and an interesting story about the status of the French army in society by itself — the army wanted to go kahki by 1910/11 or so, but loud popular opinion resisted the move).
This works for the Germans in 1914 too. Once they had been checked at the Marne, it fell to the Germans to beat an orderly retreat and stabilise a decent frontline asap. Which they did, and already at the time, and I think rightly, it was seen as indicating very high quality in the Germans opposite number as well.