So what did Hitler contribute? Was he just a frontman for the policies of the Nazis then?
But wasn't blitzkrieg conceived exactly to avoid a drawn-out war?
Hitler's Economic Principles.
It's actually more about his ideology that what he actually did. IIRC, the general consensus was that his ideological aims didn't translate into policies, which could either be taken as showing Hitler as an opportunist, or taking Hitler as more of a figurehead. However, the second one of these (the Structuralist viewpoint) probably doesn't stick in this case, as 'working towards the Führer' would have involved following Mein Kampf, and Hitler's economic principles, which didn't happen.
But then again, you could take the Structuralist viewpoint in the way of Nazi society being structured so as that Hitler was focused on his baby, foreign policy, and foreign policy alone, leaving the economy to others, who may have followed their own ideas, 'cause Hitler wasn't very interested.
As for Speer, as Sharwood suggested, being responsible for the economic policies of Hitler, that is certainly true for after 1942, or even more specifically, after March 1942 and the creation of the Central Planning Office, but before that, it is certainly not correct. Before he became Minister for Armaments and War Production, Speer was, to quote Christopher Condon, "A mere bit player in Germany's war effort." Yes, he was the closest person to Hitler, and yes he was a law unto himself in his field (the reconstruction of Berlin), but he did not have control over the economy. He was merely a department head in the Todt Organization. This, of course means that there was no way that Speer would have seized power after the Munich Pact, 4 years before he became a Reich Minister and probably 5 years before he could actually consider himself Hitler's successor (although that chance was destroyed by Speer's own petty egotism and megalomania, as well as his sympathies for the Stauffenberg Plot).
While I'm on the topic, Speer serves as a good example of how Hitler was not a particularly good leader, and how this was almost put into practice. Whilst others were a calming influence on Hitler's gargantuan plans, Speer egged him on with his fantasies. For example, the Great Hall that was to be built in the new capital, Germania, near where the Reichstag stood, was exaggerated by Hitler and Speer, combined, to the level at which it was to be built with a 300m high dome. This would:
a) Cause clouds to form in the top of the dome when the arena was filled, and
b) Deafen anyone listening to Hitler speaking, due to the noise reverberation.
Not to mention the structural problems such as the bog it was to be built on. But these obvious concerns didn't bother Hitler, who went on with the plan at the behest of Speer (although it was never completed). Basically, his judgement was severely impaired by his fantasies of grandeur.
As for Blitzkrieg, whilst it was designed to create a short war, Hitler had not wanted to implement as early as he did. When he invaded Poland, he hadn't expected Britain and France to declare war. He wanted to wait until the mid-40's before the great struggle commenced. Again, this is symptomatic his lack of judgement and impaired thought processes.
