I would agree that the American performance game is very strong right now. With the latest generation of Camaro and Mustang, they have done a good job of dropping weight and adding power, helping the pony cars handle much better. The Challenger still seems to fight on with brute force and ignorance.
My last track event, I set up in between a guy with a Hellcat Challenger and a guy with a new Camaro SS. They said they felt like they were fighting their cars keeping them on the track the whole time. They said the only time they were enjoying it was on the straight. They both left early because they said it wasn't very fun for them.
Meanwhile, my Z went exactly where I wanted it, and my instructor said that everything I did looked smooth and easy. After riding with him in his Mustang, I understood. He had to throw it in the corners and wrestle with it to get it to go where he wanted.
I test drove a 15 Camaro SS, a 15 Mustang GT, and a 15 Challenger SRT-8 before I bought my Z. I've always been a Z fan starting with my 77 280Z, and fell in love all over again with the Z33 and 34, but I knew they were down on power compared to the American pony cars, so I gave them all a shot.
Camaro, felt cramped in the interior, car felt big and heavy, power was great. Interior quality felt sub par, and the exterior looks were Ok, not great.
Mustang, interior felt good and comfortable, car felt more nimble and precise than the Camaro, power was good, and quality was much better than the Camaro. I thought it looked a lot better than the Camaro also.
Challenger, interior felt huge and comfortable, car felt very big and heavy, power was great, interior quality was about the same as the Chevy. I like the looks of the Challenger.
Z, small but comfortable interior, handling felt very precise, better than the pony cars, power was adequate, and interior quality was WAY better than the Americans. The Z is one of the sexiest cars on the road, IMHO.
The Z is not the fastest car in the world, but ultimate performance is not what I was after when I bought it. I love the style of it, love the layout and feel of the interior, love the handling and performance. The Z was a better car overall for me, because I was looking for a car I could autocross and do HPDEs in. If I was looking for something to drag race, I would have gone American. But it is kind of nice not seeing a Z everywhere, unlike the pony cars.
TL, DR: I drove the American pony cars before buying my Z, but they were not what I was looking for.