I feel with the superior arms, training, and leadership (other than Hitler, Himmler, and Goebbels) that the Germans had, the Germans could have easily ended the Eastern Front and then, as in World War I, move the German forces west in case of an Allied invasion and then maybe have proceeded with Operation Sea Lion. Everyone blames Hitler for his inept military leadership, but were there other factors involved in Germany's military defeat?
Your question is more or less "why did the german armies lose the war?". We could write a book on that.
You think of the german superiority in weaponry. To try to bring a stone at your wall, let aim at something: the german army flaws.
Yes Poland was defeated in 3 weeks, Denmarks in one day, Holland in 5, France in a month, the russian armies were pushed back to the outskirt of Moscow,... But the germans had suffered rather heavy losses while figting in Poland and in France. 36% of the luftwaffe sent in France was out of combat and 25℅ of their pilots dead. Germany's opponants were fighting and the german army was efficient but not flawless. And the Germany was always on the offensive til 1943. It put a strain upon their supply line and their troops: when a british plane was shot down during the Battle of Britain, the pilot could jump out and came back to fight with a new plane. The german pilots shot down were captured.
Some of the flaws that the german acknowledged too late (on the battlefield). Their 1940-41 tanks weren't superior. Their tanks and anti tank weaponry were limited. The Panzer III and IV with short barrrelled gun proved to be not enough against the french S35 and B1 and it would turn to be worse against the russian T34 and the kv1. The panzer III was designed to fight enemy tanks but will quickly be removed from this role and the panzer IV would receive a versatil long barrelled 75mm gun. The most common anti tank gun in 1940 til mid 1941 was the pak 36 nicknamed the door knocker because it could not pierce neither some french tanks nor russian t34 and kv1.
The latter will make the need for a heavy tank like the Tiger more urgent but this mighty beast was fragile and a high % was lost in battle because of its own mechanical problem.
Supply issues: Both in France and in Russia, the german supply was unstable partly because it as to rely widely upon horse drawn carriage. In Russia, the most famous exemple would be the lack of winter clothes.
Those are only a few exemples to illustrate than the german armies, despite being well commanded, having made a very good use of the radio to coordinate tanks manoeuvers and air support than would put the french army on its knees, relying upon well designed versatil weapons all along the war like the 88mm gun, both as an AA and an AT gun, the german army wasnt flawless and was overthrown in numerous fields, from tank design to supply.
I am emphasizing upon the german panzers because today people see them as very advanced. But like the american tank drivers in Africa, the german drivers believed they had the best tanks of their time. But after encountering their opponant's armors, they realized that tank building was well known elsewhere as well. The Russians tought us that.