A major portion of performance is based on how optimized the operating system and applications are, and iOS wins out on this compared to both Android and Windows Phone.
While yes on paper a 1520 may have better specifications than any iPhone ever released, even the latest one the 1520 has weaker hardware because it may have more cores but Apple's own A7 and A8 are more powerful.
Lumia 1520 beats iPhone 5s in Memory benchmark test, but just misses on the overall win | Windows Central
As far as the graphics benchmark you are talking about, it's flawed IMO. The 1520 can't beat a Snapdragon 801 used on the Xperia Z1, primarily because the 801 chip came with a much more improved GPU.
Plus even if the 1520 scored higher in benchmarks, there is almost zero benefit you'll have of it, and here's why:
1) The Snapdragon 800 processors heat up way more easily, and because of the heat they can't maintain their maximum clock frequency for long.
Compare that to iPhone and it can maintain cooler performance for longer, especially on the A8 chip because of the new 28nm architecture.
2) No matter how much a Windows Phone scores higher than an iOS or Android device, better quality apps and games with more effects with always be given to Android or iOS and not Windows Phone (there could be a few exceptions).