Of course not, but where did you get the 40% figure from? The error made here is comparing multicore performance to single core performance.
All the current models perform BETTER, core for core! If you were planning on getting the $10k quad core model, it's of course unfortunate that the quad option is gone. But let's try to be honest with the comparissons here, your claim is factually wrong.
Clearly you're not familiar with what constitutes a "fact." Welcome to ignoreland!
It is a fact that the Late 2012 $699 Mac Mini is faster than the 2014 $699 Mac Mini. You appear to try to gloss over that inconvenient fact by "discounting for multi-core performance," which shows you to be either uneducated or disingenuous.