I kind of go along with Hanson's view with some minor differences.  1. I think Hitler's biggest mistake was starting the war in the first place, his second was trying to conquer Russia.  The fact that 2/3 of German casualties occurred in the east is telling.  I don't think England and the US could have beaten the Germans on their own.  Mainly because they would have had a very hard time establishing a Bridgehead on the continent if Hitler had not had so many men tied down in the east.  Something like 3/4 of the Wehrmacht was fighting the Russians and even then Overlord could have easily failed.  D-day was not the slam-dunk many contemporary histories now make it out to be.  To effectively fight the Germans we would have had to be able to get at them, that takes an invasion.  The Russians soaked up troops that were then not available to fight the western allies.  Second, If Germany had been able to concentrate troops and especially their navy they could have successfully invaded England probably in 1942 after U-boat production really took off.  They could have easily controlled the Channel with 40-50 u-boats.  A German invasion fleet would have been a magnet and vital target for the British Home Fleet and the u-boots would have had a turkey shoot in the confined waters of the Channel.  All they would have to do is hover around the fringes of the invasion fleet and pick off attackers.  Another thing many authors overlook is that the battle of Britain was unnecessary from a military standpoint.  The Germans did not need to achieve total air supremacy for an invasion, they tried for it anyway.  All the Germans needed was local superiority to protect their invading forces until airfields could be established ashore which would have made the relatively low endurance of German planes less of a factor.So yes, I think the British and Americans needed the Russians just as much as the Russians needed the Western allies to successfully win the war.  This analysis ignores nuclear weapons, but given that they were not operational until 1945, I think nukes can be safely discounted, Hitler would have solidified his control of Europe by then absent an Eastern front and it would take more than the 2 nukes available to defeat him.

As a continental power, germany did not need a blue water fleet.  If the conquest of Europe had been consolidated, Hitler could have made a variation of Napoleon's continental system work, especially if he had been able to successfully subue the Soviets.  All the Nazis needed a navy for was to control Englands coastal waters, enough U-boats concentrated in British home waters could have achieved this.  England would have been forced to the negotiating table.  As it was, I think it was in 9143 that England was down to less than 2 months supplies of strategic minerals and foodstuffs, until American naval power made itself felt.  The Battle of the Atlantic was closer thing than many realize.