The 360 would have 192 shader units by AMD's current way of counting them but they were a first generation implementation of unified shaders whereas 4xxx series products were AMD's 4th generation implementation. Even a 160 shader part (dual SIMD) from that generation should have little trouble achieving higher real world ALU throughput especially considering the much higher clocks they can run at.
For reference, AMD have started shipping midrange CPUs that integrate a 400sp part on die. Coupled with the right memory setup, that sort of chip could absolutely decimate the 360 in graphics performance with a a modest 50-60w TDP. I could understand why someone would call that a modest upgrade over 360, heck the theoretical CPU FP performance will probably be decreased , but you're still looking at a system that should be capable of running this gens games in 1080p @60fps, with much higher resolution textures when deployed in a closed box.
If you don't think that's a large leap forward then you're going to be disapointed by the other machines, as there's very little chance the jump from this systeem to them will be any bigger than the jump from the current generation to it.