That notion has been made by other sources. Germany might have been able to prolong the war, but it still didn't have the resources to crank out arms/materiel like the Allies. Therefore many other experts, including Churchill, concluded Germany was defeated as soon as it declared war on the U.S.
I think if Hitler never back-stabs Stalin and attacks the USSR- Hitler wins. I don’t see anyway the Allies break into Europe without his forces spread into two fronts.