Why did they have to wait over 40 years to attack?

Even during WW2, the Germans had 'engineering supremacy'. Their tanks and planes were built far better than anything the allies or Russians had. Unfortunately, they couldn't build them fast enough, so they were beaten by the sheer numbers of cheaper and quicker built equipment.

It’s ridiculous to critique a movie with the argument 'it's not real, so it doesn't matter'

While that may or may not be the message of the film, you misunderstood the cause in real life.

In real life, the actual reason is because an economy that is isolated from the rest does not have the ability to engage in free trade, which expands the production frontier and increases economic capacity. Since the Nazis were poorer, they were likely to have poorer technology as well, even leaving aside the benefits of scientific exchange with other countries.

Yes, the Germans, for all their "superiority" hadn't advanced scientifically or technologically since the 1940s. How they managed to land on the moon in the first place is a mystery, but once there, they were pretty much stranded. Even their best scientist kept delaying the launching of their finest war machine.

In a way, it's a commentary on isolationism and focusing on the wrong things (racial purity). On the other hand, "German Engineering" on Earth is a pinnacle of quality, perhaps post-WWII because they were free to focus on a variety of great products instead of ideologically driven technology.