It is actually quite interesting to see the various factions and their points of view. There is such a theological war that only a handful of individuals have any real information on which to base their heartfelt convictions.
As an economic fact you can certainly replace 1,000 blade servers with 1 mainframe. What you end up with will be MUCH cheaper to buy, more reliable, and infinitely simpler to maintain; ok, not literally infinite but when you're paying for 90% fewer administrators you might think it pretty infinite.
Mainframe performance is Extremely hard to quantify in PC terms. Largely this is due to the co-processors that do so very much of the ancillary work in a mainframe complex. PCs have started to enter this world some with the longest standing and best example of course being the GPU. But for the most part the CPU still does all the work itself.
Just as Intel has been trying to escape the clock speed trap for 5 years or more, mainframes just don't have such a "general public" graspable "speedometer". MIPS are surely at best arbitrary. There are MANY standard performance measures of "typical" processing, whereby such things as database access, or the "typical business transaction" [yeah right] are modeled. But none of these are as cozy as: "2GHz is twice as better then 1GHz " [sic]. Regardless, it would be much more accurate and fair to say the Intel hawkers have avoided such comparisons knowing that the results will not show them in a positive light.
Of less importance to Reg readers, but of huge importance to the industry as a whole is the OS itself. z/OS for all practical purposes simply doesn't fail. It is perfectly suited for applications involving human life, financial transactions, or anything else that really actually matters. Unix (Solaris etc) of course are equally (or nearly so) high quality. And Linux has made remarkable progress and now stands quite respectable as well. The real concern from an industry perspective is Microsoft. IT people who want to go home at a reasonable hour and then sleep through the night are best advised to not put "things that matter" on a Microsoft platform. But many people who think "computer" means PC and "OS" means Windows make a terrible mistake and cause real, often fatal, harm to their business simply because they "Don't even know that they don't know the right question, not to mention the answer".
So, we will never have a single hardware/software platform any more than nature will settle on the one perfect organism. But that doesn't mean IBM / z/OS should not dominate in many areas. Nor does it mean that natural selection should not weed out Microsoft from the food chain.