You are not seeing the full picture, do you ?
Console manufacturers always end up finding technical efficient solutions to do things at launch time, only very expensive PCs can do. It has always been like that. True the xbox360 GPU was relatively more powerful in its time compared to the ps4 GPU. But what about :
- CPU - GPU interaction and bandwidth ?
- RAM quantity and Bandwidth ?
We are talking here about a UNIFIED 4 Gb of GDDR5 at 192 Gb/s (remember PC games use nowadays DDR3 RAM, how they could compete with first and second gen ps4 games designed with GDDR5 main RAM bandwidth in mind?), if true thats incredibly monster RAM architecture, far a lot better compared to the PC landscape today than the disappointing 512 Mb at 21.6 Gb/s of the xbox360.
Also having a SOC with CPU+GPU on the same chip allow to overcome any previous bottlenecks of PCs PCI express interaction bandwidth between the CPU and GPU, and xbox360 didnt have that advantage compared to PCs in its time.