Your own reference disputes what you are saying. From the referenced page:
"However, newer, partially or fully configured System z machines outperform Hercules by a wide margin"
It is quite clear that Hercules on a moderately powerful Intel based system can outperform a historical 360/370 architecture machine, but that is not a modern 64 bit zSeries system. IBM continues to persuade their customers that this is the case with worked case studies, and if you believe their 50th Anniversary presentations, they are even winning new customers to their mainframe platform.
One of the differences is that a zSeries system is designed to run at 90%+ CPU utilisation all the time, and with a high degree of resilience and exceptionally low downtime. What x86 plaudits continually fail to recognise is that such a system will keep doing this while CPUs fail, memory drops out and other hardware events happen. Commodity x86 hardware does not have the Enterprise RAS features to do this, and the Enterprise grade Intel based systems with some of these features (like the remaining Unisys or HP Integrity systems) approach the zSeries in cost because these features are expensive to add.
There will be a time when x86 based systems will have the types of RAS features that zSeries has had for some time, but I don't see it being now, nor any time in the immediate future.
And anyway. I don't want to see a world where one processor type has a virtual monopoly of all systems sold. IBM with the zSeries and POWER, and Oracle with SPARC derived processors are holding out for the moment, and I hope to see 64 bit ARM processors in the market at some time. There has to be some competition against x86, because it always has been a flawed architecture.