I'm left wondering what you call the "drive train". Since, certainly, the Coyote motor is considered world-class. And the brakes and suspension are great. Not perfect, but great. Again, Mustang (Brembo PP/Track Pack) lap times are identical to those of the M3. Yes, the shifter mechanism is crap and many replace them, but that's why the car is 1/2 the price of M3s and such.
As far as you not thinking Mustangs are true "drivers cars" like an M3/911....well.....you bought the wrong Mustang. You didn't buy the "driver's car" Mustang. So, your opinion is based on the wrong car.
And no, Mustangs are most definitely NOT muscle cars, not even close. And the term "Pony cars" is a marketing scheme, nothing more. To be precise, Mustangs are Sports Coupes, as are 911s and M3s.
Yes, M3s/M4s and 911s are far more refined and built better, but that's where the price difference comes in.
You are confused what cars are in what class.
Mustang = muscle car, period.
Porsche 911= sport car, period.
M3= luxury sedan/coupe or you could go as far as saying luxury sport.
These 3 cars are in NO WAY related and all 3 of these cars were built with different purposes in mind.