There's more to a car than power/weight ratio and handling. Believe it or not, it does matter to some people (Me!) how common the car is, but that's besides the point. Back seat space is a huge deal. In the stangs, you need to be pretty tiny to be comfortably behind someone who is of average height. A coworker of mine recently bought a Challenger, knowing that it is the slowest of the modern muscle cars, because he actually fit it in comfortably!
Also, in the used world, the Fords tend to hold their resale better. A few years ago I was hunting for a muscle car; 06 GTO vs 07 Mustang. The GTO was 3k cheaper and was way more comfortable.
Point is, it's different strokes for different folks. Those who say Camaros are slow and handle like shit, don't be surprised when someone blows by you in one because they bought it just to throw people like yourself off, and spend 10...20...30...40k on upgrades. Dang I wish I had that kind of money.