With regard to the specific instance of Poland, it isn't completely inaccurate. It just ignores the context and that it makes it fantastically stupid.
True. America's involvement was crucial in limiting Russian influence in Europe at the end of the war. The outcome of Germany's war was effectively decided the moment he attacked Russia. It might have taken longer and been messier but the result was only going one way.
As you well know, he was told by his senior naval figures that an attempt to invade us could well have ended with complete disaster. The Kriegsmarine was in no shape to protect an invasion fleet from the Royal Navy, having lost a lot of its destroyers in Norway and, even if the Luftwaffe had had air superiority, the losses the Grand Fleet could have inflicted on an invasion would have been potentially disastrous.