Ok, I will admit, I forgot they are Cup cars and not Spec Miatas. So my bad. Face palm accepted.
However, after checking a few facts ... guess what. It's MY G-D car!!! The only difference between my car and a Cup car is that the Cup car is allowed to use racing mf tires. I'm using street tires. (well, and one other notable difference, the roll cage and lack of a heavy ass hard top which raises my COG.)
So, in review, I drive an MX5 cup car (close enough) to work every single day and on the weekends on the track. I have video, posted here, of me flogging the hell out of it with throttle buried to the floor without spinning. I am glad that you find it easy to drive. To me it drives nothing like the car I drive. It's a completely foreign animal. And I will say, that if you take the stock NC in GT6 (not the GT6 MX5 Cup car), bolt on a racing suspension, put on sports soft tires ... the car drives as I would expect it to. You can tune it and it behaves exactly like my car does. The GT6 MX5 Cup car takes that a step further (although, there is something off about it, can't put my finger on it).
So no, I have not ridden or raced in a completely spec'd MX5 Cup car. However I am following a build over on TrackJunkies .org by the CJ Wilson Racing team. I know what goes into one. You can also read more about it here:
http://www.mx-5cup.com/2012/inside/index.php#car