I your point misses the obvious benefits and experience that come from doing actual operations on a massive scale and under real fire. The biggest challenge in training and in drills is making them realistic and large enough to seem real and to reveal actual problems, kinks, etc. You think your drills will come close but they never really come close to what the real thing is like. The Wehrmacht in 1939 got to invade another country whose troops were going to shoot back live ammunition. That means the Wehrmacht has more chances to see and fix mistakes in their operations and their troops get to see what real death, wounds, mobility, etc. look like. By that standard they are "veterans" in a way no Frenchman or Brit was in 1940.
It does not take long (in 1930s terms) to build up a trained military, especially not when you have a professional and experienced cadre and believe war is coming (even if not imminent). The US did it in two years and the Russians rebuilt a vast army in less time (out of necessity). The Germans started training and rearming from the early to mid 30s when most of the rest of the world did not want to take seriously the prospect of another war.
"Experience" can be as harmful as it can be beneficial. By virtue of historicity, it is entirely possible for campaigns to yield all the wrong lessons learnt and/or induce doctrinal stagnation, especially so if there is an outcome deemed successfull enough. This applies not only to "splendid little wars" (ie. the British military pre-the second Boer war), but also to large scale conventional conflict. Consider ie. the example of the pre-Napoleonic Prussian army, or the French military prior to the Franco-German war, whose development was arguably rather retarded than helped along by having fought two recent campaigns against peer competitors plus a number of glorified colonial policing actions... The Ottoman military pre-WW1 also makes for a particularly good example, and I could go on at length here.
Even in the realm of infanteristic combat, experience need not necessarily correlate to competence. If you ever had the displeasure of witnessing (at least some) African paramilitaries in action, I guess you'd agree. The Germans started rearming at scale only from 1935 onwards btw, and had a giant deficit to bridge to start with. One of the reasons for the scepticism of the higher German command echelons vis the Westfeldzug (look up the Generals' meeting from August 4th, 1938) was owed to the fact that they felt everything but thoroughly prepared for it, as indeed they were not.
Resources in shipping does not help you either getting onto the land or transporting it from those landing points to an ever farther front line, especially if you have to land new troops at the same time (and then the material for those new troops, etc. etc.) To use the prior analogy, you have the 100,000 sq meter warehouse and lots of forklifts, but still only one loading bay. That is why the only major offensive in the fall of '44 was Market Garden, and even that, by the standard of most offensives was not actually great. It stands out because it was a very "dramatic" and ambitious operation with a involving massive airborne drops. And to accomplish even that the allies had to hold off on all other operations for a couple of weeks, giving the Wehrmacht desperately needed breathing room.
Well yes, even the Allies were running out of logistical steam in the fall of '44, but consider this in the context of the logistical possibilities possessed by their adversaries, which amounted to quantité negligable in comparison. Something like the Red Ball Express was quite simply out of the question for the Wehrmacht since even in their heyday, they never remotely had the same degree of motorisation and relative resources at their disposal.
Don't get me wrong, this is not meant to diminish the Western powers' logistical archievement in Normandy, after all it was the largest amphibical op in the history of mankind.
The contention had been that the Germans had been brilliant in defense in the latter half of the war and they only lost because that brilliant military was overwhelmed by sheer numbers in men and material. Their defense was not brilliant or they would not have had effective forces decimated one after the other. Bagration cost them about what Stalingrad did. And another 100,000 were lost in Normandy prior to the Allied breakout and the disintegration at the Falaise Gap.
It was a very expensive July.
I don't think anybody would seriously wish to dispute that "sheer numbers in men and material" was the single largest factor in the eventual Allied victory, and if he would, I think he would face a very much uphill battle in construing a plausible argument to that end. However, the fact of overwhelming Allied numerical/material superiority does not necessarily prove or disprove any particular defensive "brillance" - or lack thereof in the German camp.
Considering the two operations in question beforehand (Normandy/Bagration),
in Bagration, at the strategic echelon, you have the archmistake of leaving HG Mitte overextended in an indefensible position for essentially political reasons combined with an unhealthy dose of wishful thinking, ie. choosing to believe FHO despite ample evidence from local commanders and HUM/SIGINT over the Soviet buildup, thereby misjudging the direction of the Soviet thrust, leading to inevitable catastrophy.
In Normandy, the constellation is not fundamentally dissimilar, insofar as the leadership failed to see the writing on the wall and still insisted on attempting to contain the Allied landings forward even though the attritional picture had clearly become unsustainable and it could only be a question of time when this unfavourable situation would translate into large scale Allied operational maneuver - the rest is history as they say, the German lines being unhinged and the retreat devolving into a general sauve-qui-peut all the way through France.
Still, given the asymetry of forces and the overall limitations of the Wehrmacht, its performance at the tactical and operational plane remained surprisingly credible; even managing to contain the Allies for as long as they did and inflicting equivalent losses was a considerable feat by any standard, and while July was a costly month indeed for the Wehrmacht, and Bagration was undoubtedly the most traumatic defeat suffered by German arms in the 20th century, it was costlier still for the Soviets.
But it was always largely an unmotorised force. [...]
This has essentially already been answered. The Wehrmacht was even at its zenith indeed always an army characterised by a strong asymetry in mobility and operational tempo between its mechanised maneuver element and really, the rest of it, however, it suffered a stark, gradual degradation over the course of the war, while its opponents were either fully mechanised from start to finish(Commonwealth/US) or continually improved in that regard. (the RKKA).