The history behind the design of OKW is bogus. The personnel quality of German formations in 44' were lower than those of 43', and those of 43' were lower than those of 42'. The Wehr peaked in 41' in this area.
The winter 1944 German elite divisions were generally a thin strip of veterans from earlier battles bolstered by the majority: green conscripts age 18-16 frequently. Generally 3 months of training or less prior to the Ardennes offensive. The damage caused by the offensive was mostly the result of strategic surprise and deception rather than formation quality.
Not necessarily. While the overall strength of the German Army wasn't as strong as it was from 39-41, it did have the benefit of having Panzer SS and Heer divisions that were extremely skilled, and had a considerable amount of experience in battle. When the Allies started their campaign in Western Europe, German high command transferred divisions/men who fought in nearly every major battle in WW2 to reinforce Western Europe's defences, so I definitely think the title of "elite divisions" is appropriate and why that persona fits the OKW perfectly. Another thing to take into consideration is that some divisions performed well above any Allied divisions, while others didn't enjoy that same success, so you're correct in stating that not every German division were elite formations.
There's countless battles in WW2(On the Western Front) where Panzer SS divisions faced off against Americans who had more men, resources, tanks, planes and etc and won, so we do have to give credit where credit is due; Relic sought to make the OKW a faction based on Panzer SS and Heer divisions during the Western Front and it reflects that I think. Germans on the Western Front from 41-45 didn't have the manpower, resources, tanks, artillery numbers that the Allies enjoyed, but they made up for that with extremely battle hardened troops, superior training, weapons and tanks.