Actually, taking away that hindsight advantage could be done in two ways:
i) Removing every single bit of historical scripting, so you won't know what to expect. Would that still be WWII? Of course not.
ii) Making the AI make all the minimax optimal decisions. Would that still be WWII? Of course not. Germany would probably be attacked by the Soviets at the moment they start going into France, which would have twice the strength as historical.
the first diplomatic AI I did for HoI3 actually had an EU3 style min/max style. it was pretty impossible to get anything historical out of it so we fell back to much tighter scripted solution with events and country specific decisions.
Fewrfreyut made a good post too. it would be interesting to have a game where in reality there are parts of the government pulling in different directions, not following orders properly and having their own crazy agendas (its generally thought that Hitler had some skill with strategy but lost his marbles more and more as the war progressed and same with many of the people he surrounded himself with), but i suspect it would be very frustrating to play a wargame like that