The Germans did indeed have huge losses fighting on two fronts during WWI, but they were so superior to the French and British and Russians that they were losing only about one soldier to two of the enemy. That is why they were actually winning the war and the USA had to intervene.
But they weren't winning against the rest minus the US by a year later, even though the US had not had time to get in seriously. Russia was beating them, and beat them. The Germans had the overall potential to defeat Russia, but out of overconfidence did not think they would need it and failed to fully mobilize their production to support a major land war of attrition when they attacked. They hoped to defeat Russia faster than that, a hope that proved naive. They only gave up on the idea of cheap victory there at the end of 1942 after the Stalingrad counterattack. At that point, they were already losing the war. It was largely the Russians who beat them. With the US in as well, the outcome was as they say "overdetermined" - they didn't have a prayer against both.
LOL way to rewrite History, America did not intervene, Japan attacked you and Germany declared war on you.
And if you are really interested in the merits of all the fighting men I recommend Max Hastings Armageddon.
There are conflicting reports but most agree about 3/4 of German losses were on the Eastern Front fighting the Soviets.
The Germans and Soviets when well led made better soldiers, coming from dictatorships where life was cheaper, they were able to withstand the horror and death of war. many also were brought up in martial environments the Hitler Youth and Kommosol both had a strong death and glory cult
On the Western side many had to overcome religious and western liberal upbringing before they could pull the trigger.
"The Germans ... were so superior to the French and British and Russians that they were losing only about one soldier to two of the enemy."
Equally true of the American Indians whenever they were in fights in the woods.
The bigger truth is that German military thinkers were so stupid that they attacked enemies who outnumbered them 5:1.
So they got creamed.
Didn't learn.
Did it again.
And got creamed again.
That's not just not brilliant, it's apocalyptically bad, titanically incompetent.
The Germans showed some tactical capacity and made some gains in ground warfare. That usually happens when you attack first.
At sea, the Germans were pathetic.
In the air, they were inferior to the French in World War I and the British and the Americans in World War II, not just in numbers, but in overall capacity of operations. The German commanders did not understand either airpower or seapower, and squandered what they had.
In ground forces, German units were good tactically. Strategically, they ranged between mediocre and catastrophically bad. The only truly stunning German military victory was France, 1940, which came about because the French high command was even more incompetent than the German.