If you have the Brembo/track package the stability control is much more forgiving than the standard system. In sport mode, there's even more "freedom". But, it is quite magical in how it works. If the track is rain soaked, I put the car in sport mode. It saved me from myself on multiple occasions.
Now then, the backend can get loose, but, it won't "fishtail" much. To disable it completely, have the car running, put foot on brake and press the TCS button and hold it down. After about 30 seconds it will display "AdvanceTrak disabled" (or "off" I don't recall).
I will add, when I first started reading this forum, there were several cases of people driving around with AdvanceTrak off and sending their car off the road. The Coyote engine above 4000 RPMs is just a beast. Randomly stabbing the throttle can lead to unplanned adventures. The AdvanceTrak system can be very helpful.
I do agree with everything you said about the desirabilities of AdvanceTrak. I do have a Track Pack car, and I have no need to turn off the nanny. It's my wife's daily driver. I just noticed it getting loose where it didn't before so I wondered if I was having a problem with it.
It seems it's more than likely the temperature dip as of late has revealed the shortcomings of the stock tires. I'll know for sure in a few days as my 2nd '14 GT TrackPack will be delivered tomorrow and I can compare.
Thanks for the input.