You obviously have no idea what you are talking about. x86 is only the ISA of the CPU, but Zen 2 (the micro architecture of the new consoles‘ CPUs) ist vastly different from Jaguar (old consoles). Also RDNA 2 (new GPU architecture) is massively different from GCN (old GPU architecture). The consoles each have additional custom functionality and the overall system architecture is very different from the previous gen. Each generation of hardware is different and devs have to get learn how to make good use of it. There are new APIs, the CPU and GPU have improved instruction sets, latencies of those instructions are different, memory and caches behave differently etc. There is way more to these new consoles than just the ISA.