Hitler interfered and fucked up a lot, however Germany was never close to winning WWII. It was never in the bag. Hitler and the German military leaders knew their only chance was to win a quick war with the Soviet Union. Despite the massive early victories the Soviet Union kept fighting and Germany was doomed to lose a war of attrition. And they did lose a war of attrition. Once they were turned back at Moscow the war was lost even though Germany was still winning in terms of territory captured and equipment/troops destroyed.

Hitler did screw up on the Normandy landings, however by D-Day June 6, 1944 the war was already lost for Germany. The Germans and Italians in North Africa had been beaten and surrendered. Most of Italy had been taken and Benito Mussolini had been removed from power. The Red Army had soundly defeated Germany at Stalingrad and Kursk, the Siege of Leningrad had been lifted and in the summer of 1944 Operation Bagration pushed the Germans back to the former Polish border and completely destroyed Army Group Centre.

The only way Germany could have won would be if the Soviets had crumbled but unlike the French they were unwilling to grab their ankles and bend over.