first of all, had the US been neutral in World War 1, Germany would've won
No, with or without America we would have won anyway, it would have taken certainly more time for the French and the British to finish this war. But the western front has never been broken, in the latter days of ww1, only one time the Germans advanced during the Chemin des dames offensive in 1917, but after the second battle of the Marne, a counter attack of the French initiated in Villers Cotterêts devastated the German forces, and this marked almost the end of the war for the Germans, their Austrian allies already surrendered, and revolts began in Germany against the Kaiser.
second, it was the Americans who completely took over the Western front of World War 2. The Germans only declared on the US because fucking Japan had to bomb them
No most of the German generals were against the declaration of war, Hitler was an idiot, if the western front was successful it's only because the Germans wasted all their armies in the Russian front. So you should thank the Russians and Hitler's dumbness.