The Xenos (360 GPU) was actually more advanced than the X1800. The X1800 still had vertex and pixel shaders:
http://www.anandtech.com/show/1810/2
Meanwhile the Xenos was the world's first consumer GPU with unified shaders. We couldn't buy a GPU with unified shaders until the GeForce 8800 in 2006 (a year later). Even if in 2005 the X1800 was on paper faster than the Xenos by the end of its life the unified shader advantage was huge. We see that when modern engines are run on old GPUs- here is a 8500 GT (a barely mid level GPU but had unified shaders) beating a 7900 GTX (the high end GPU from the generation before the 8500 GT with dedicated shaders):
I am sticking to my guns: The Xbox 360 was the most advanced GPU you could buy when it launched, and PC GPUs couldn't beat it until a year later. The PS3 on the other had actually had a less advanced GPU than the 360 because Sony had to bolt it on last minute.
It makes a lot of sense when you put the economics of PC gaming back in the equation. The flop of this year's batman game showed us behind the curtain, and we see that the PC port got a FRACTION of the human resources the console version got. It doesn't matter if the PC is way more powerful if the PC port is so unoptimized that it produces the negative of the "to the metal" effect.
Directx 12 can't get here soon enough, even if it turns my GTX 970 into a pumpkin.