There are reviews going back to 1977 that specifically mention the ending being straight out of Triumph Of The Will, which is where the inset image is from. I had no such frame of reference as a kid, so had no idead what the critics were talking about.
When I rewatched the Flash Gordon serials a few years ago, I noticed Ming The Merciless goes from looking like a oriental villian in 1936, to dressing like a fascist dictator in the final story from 1940.