1) I answered your question by showing that the gamble was a bad one. The Germans were making the equivalent of having no cards at all to bluff a very strong hand, and this is why they ultimately failed both times. We should not believe the self-serving lies of Germans and Allied generals. The German army in both world wars was a bunch of feuding nincompoops incapable of adhering to their own plans. The Allied armies were led by bigger nincompoops sometimes surprisingly incapable of even knowing how to formulate a plan. Bad plan beats no plan.
2) You are missing that the British Army of WWI was a mass army of first volunteers and then conscripts? An intact BEF has no impact one way or the other on quality, there's not enough BEF for that to happen in the first place. The Pals were going to dilute the WWI British Army regardless of what did or did not happen to the BEF.
3) Neither German army had any kind of logic in what they were doing. This is in fact a major reason why they lost in mistaking opportunism for an enduring actual tactical foundation. For instance the statements of the Germans wanting more territory in a Race to the Sea that was not a race nor aimed at the Channel, but instead the results of both Allies and Germans trying and failing to outflank each other.
4) Yes, I've read their plans. They decide to bulldoze through Belgium, deleting their additional decision to do so in the Netherlands, and by magic advance over a very long distance in six weeks and defeat the French by virtue of magic. The plan did not account for potential actualities in a war situation and was very clearly designed by a desk jockey. That Germans lied and claimed some infallibility from what actually happened, which was a botched attempt at a double envelopment held on *both* ends is not a reason to believe similar lies about the all-knowing Alfred von Schlieffen.
5) Well you could try refuting it by showing where WWI Germany ever showed any comprehension of strategy or logistics against something that wasn't an overextended third rate power, for one thing. Or alternately actually showing this mythical self-serving lie of German brilliance existing as opposed to being a Big Lie to cover up how bad Allied armies in WWI were. While Germans of course had no problem accepting that they were stabbed in the back by dirty Jews and Commie scum as opposed to defeated in actual fighting.
6) No, they actually didn't. This is one of the many Big Lies about 1940 that tend to proliferate, and their actual margin of victory in the Ardennes is narrow enough that a very slight increase in artillery, no infantry or air power is all it takes to derail the whole thing in practice. If people would rather believe that democratic armies can't fight totalitarian ones on the battlefield then that's their problem. This is no more true than saying that Thomas's attack up Missionary Ridge was a brilliantly-planned stroke or that Erich von Manstein won the Kerch Campaign as opposed to Lev Mekhlis bringing the Reverse Midas Touch. Something being generally accepted by mythological historiography is not true because it's generally accepted. You could, for instance, name where Ritter von Leeb scored these penetrations and provide links, but you'd rather engage in talking about talking.