Dennis Wilcock did 9/11
Exactly my thoughts when I first heard it. At the time, AC/DC or even Motörhead could do a whole song with a basic riff, and Priest was doing some pretty simple stuff, and Maiden came out with songs litteraly cramed with fantastic ideas. Genghis Khan or Purgatory are fantastic in that respect.
This sharp contrast in approach is the main reason Iron Maiden is, indeed, a heavy prog rock band in many aspects. They drew a lot of influence from blues-influenced rock bands but they eradicated most of that blues influence when it came to their own style, their stylistic approach has always been closer to prog rock.