Mustang = "Muscle Car" vs. "Pony Car" vs. "Blah Blah Blah"
There is not now/never has been an official "Muscle Car Validation Organization", so the argument of what is a muscle car will continue until the end of time.
Except from 2003-2009, when they stopped making Camaros.
Quarter mile times are directly related to/indicative of a vehicles 0-30, 0-60 times etc. That's common sense. Regarding the '15 Stang ...
Having yet to see one in person, this pic represents my current thoughts on the matter: