You have a great many sources but no cites.
Which is a little better than a great many opinions and no sources
In terms of the CER.
The Germans, being outnumbered (which is now evident from Zetterlings detailed analysis of unit strength, one of his biggest if not biggest contributiuons to the debate) inflicted a higher percentage of casulaties on the allies in proportion to their numbers than the allies did in reverse.
That's what both the CER and CVR do, they factor in the reality that having a superior number of combat troops over an opponent confers a big positive non linear advantage that is roughly a 'square' factor. Other factors incorporated are the advantages of defense over offense.
I dont know about Zetterlings numbers analysis, but there are many sources that give ratio of forces and casualties suffered. One source is the Portsmouth Historical Institute, another is the American Historical Association, but there are many others, more substantial than those, including many in print. Whilst it should be acknowledged that accurate figures for losses and numbers are imprecise at best, even taking into account Zetterlings work, its a very big stretch to argue that the Allies outnumbered the Axis in terms of frontline strengths during the campaign. For example, the Portsmouth Institute says that on the first day the allies managed to put ashore 100000 men, and suffered 9000 casualties (not all of them permanent, or fatal ....the estimated permanent casualties were about 5500, of which about 2500 were suffered at Omaha). This source puts German/Axis permanent casualties at an estimated 13000 men. The combat strength of the Allied forces on that first day reached an estimated maximum of 39000 men, they were faced by a total of just under 100000 German troops (say a frontline strength of about 55-60000 men). Saying that German formations in the West were understrength , prior to engagement is not supported by facts. The Germans on the Eastern Front had formations that were running at about 40% authorised strength, but on the western front, prior to Normandy, the germans were using this front to rebuild their formations. Most formations in France were at 90-100% TOE strength on the first day of the campaign. As the battle progressed, the rifle strengths of German formations took a nosedive, mostly because of the interdiction campaign whereas allied formations could be rested and rebuilt. But thats a function of the campain, and a terstament to the effectiveness of Allied all arms warfare, not to the superiority of the germans on the battlefield.
Moreover, it took some time for the Allies to overtake the germans in terms of frontline and total strengths. According to the US online History website, "By nightfall on June 6, more than 9,000 Allied soldiers were dead or wounded, but more than 105,000 had made it ashore and secured French coastal villages. Within weeks, supplies were being unloaded at Utah and Omaha beachheads at the rate of more than 20,000 tons per day. By June 11, more than 326,000 troops, 55,000 vehicles, and 105,000 tons of supplies had been landed on the beaches. By June 30, the Allies had established a firm foothold in Normandy. Allied forces crossed the River Seine on August 19.
Moreover it was not until the third week of the campaign that the Germans were overtaken in terms of numbers. by June 11, the estimated frontline strength had reched about 400000 men. 39000 men were lost outright when Cherbourg fell. Panzer Lehr lost 2000 men in a single day. There were never anything like those casualty rates suffered by the Allied forces in any part of the campaign
Your position here moreover, seems to have shifted. You started out by saying (or at least implying) that Allied casualty rates were twice that of german rates. Clearly the data that we do have does not support that. The Germans appear to have suffered around 425000 casulaties through to the end of Falaise, compared to somewhere in the order of 209-235000 Allied casualties. You have not responded to, or refuted those numbers, though you are sticking to the line that Germans were killing twice as many allies as the allies were inflicting on the Germans. I cant see how that can be sustained when a maximum of 1.4 million allied soldiers were deployed to the theatre in the time frasme, and less than a fourth of those were frontline combat troops, yet they managed to inflict casualties of around 425000. I cannot see how it can then be claimed that allied loss rates were twice that of the germans, or that they outnumbered the Germans in terms of frontline boots on the ground.
The Germans, with harsh and bitter experience from the Franco-Prussian war, WW1 and WW2 were extremely effective, organised and well lead fighters. In fact their experience goes back to one of the greatest Military analysists and strategists of all time von Clausiwitz who coined the phrase 'the fog of war' and developed the concept of skirmishing to a high level after he went to work for the Tsar as a way of fighting Napoleon after yet another French invasion.
The germans had a fine military tradition and a solid basis from which to build their army, these are valid issues to consider. So too did the British Army. The other allies like the americans and canada, had less in terms of military traditions, but they were excellently trained, led and equipped, and were imbued with a fighting spirit at least equal to that of the germans. There is no evidence to support the notion that the younger nations that participated in the fighting were in any way handicapped by that.
Working against the Germans was their very limited equipment levels, the large number of caualties their army had suffered by 1944, the supply shortages they were suffering, the fact that a significant proportion of their formations werent even German in nationality (with motivation issues that went with that). other formations like certain SS formations were excellent in motivation, but poorly officered. Other formations had virtually no transport, and the list goes on and on.