Being RWD it won't corner anything like the RS. But I don't think it's like the old ones, which would go all over the place when you put your foot down
You can still expect at least one brown trouser moment in any powerful RWD car though if you drive it quick.
I still see there is common miss-conception over American cars and how they handle.
Yes the Mustang out the factory has many short comings in stock form, most of all being the absolutely shocking Pzero tyres, there are many here who also have Pzero on their BMW's and Porsches who share the same thoughts, the tyre is terrible in cold, wet conditions and even the dry grip in the warm is nothing to shout about and then to top it all off they don't even last that long.
Anyway some lap times from Hockenheim Short circuit driven by the same driver:
Mercedes-Benz A 45 AMG Christian Gebhardt
1:13.50 380 / 1574
Audi RS6 Christian Gebhardt
1:13.70 560 / 1895
Ford Mustang GT (Mk VI) Christian Gebhardt
1:13.80 426 / 1650
Alfa Romeo 4C Christian Gebhardt
1:14.00 240 / 895
Chevrolet Camaro SS (Mk VI) Christian Gebhardt
1:14.00 453 / 1666
C63 AMG T Performance Package Christian Gebhardt
1:14.20 487 / 1795
Ford Focus RS Christian Gebhardt
1:14.20 350 / -
Audi RS4 Avant (B8) Christian Gebhardt
1:14.30 450 / 1755
Maserati GranTurismo Sport Chistian Gebhardt
1:14.50 460 / 1780
Porsche Cayman (981) Christian Gebhardt
1:14.50 275 / 1310
Dodge Challenger SRT-8 Hellcat Christian Gebhardt
1:14.60 717 / 1892
Jaguar F-Type V6 S Christian Gebhardt 1:14.70
380 / 1614
AWD does not make you corner faster, it makes it easier to go faster particular when conditions are not ideal and they require less skill behind the wheel. Having owned an EVO X with 415BHP which would for sure take down an RS in any conditions on any road or track and I can tell you now the 911 and Mustang on a dry road or track could take the EVO X down. Talking from ownership experience here, not Mr Armchair expert. In the dry it is far more down to chassis setup, feedback from the car and overall mechanical traction. On a dry circuit or dry road with professional drivers (removing driver from equation) a Mustang will corner every bit as good as a Focus RS if not better. Quite an accomplishment really as the Mustang stock has a lot of short falls due to the tyres and soft/bouncy rear suspension.
Any car can be improved but percentage improvement in the Mustang is higher simply because Ford could have done such a better job from factory but the GT Mustang was the cooking edition, the Shelby was the properly sorted handling one and you can quite easily get a GT handling like a Shelby, tyres, coilovers, anti-roll bars and some solid bushings in the rear for about £3000 including tyres, actually better as the Shelby too has the same soft rear-end and other short comings and a lot of owners go and fit same parts as I've done to mine.
Wet day, cold greasy day give me an EVO X or Focus RS any day if my aim is to drive fast and get from A-B as quick as possible. Otherwise the Mustang works fine in the cold and wet, its vastly improved now its on MPSS tyres but you just drive to the conditions or you do massive skids everywhere.
Also the term handling, I'd take most RWD cars as better handling any day of the week, handling and grip are too different things. The Focus RS, EVO X have loads of grip and they also handle nice and are very much point and squirt. But my involvement, concentration and fun factor for me in RWD is on another level.
The only modern American sports/muscle car that still handles like a true muscle car is the Dodge Challenger. The new Mustang and Camaro are fantastic handling sport coupe muscle cars and incredible value!