With a V6 the ATS is over 3600 lbs, so I'm skeptical an Alpha Camaro will be much lighter than a Mustang. It will depend a lot on size, seeing how the CTS can be over 4000 lbs on a long wheelbase Alpha platform too.
Even so, the Challenger is a much, much bigger than the current Camaro and Mustang and has a good deal more content. If the Camaro becomes the size of an ATS it will be even smaller, while the Challenger can haul 4 people and their stuff comfortably.
I've also come to the conclusion that someone will always find something wrong. They delivered a full - size car with 707 HP, 3.5 sec 0-60, 11.2 second quarter mile, 200+ mph top speed, with 20 mpg, a luxury trimmed interior, multiple configurable drive settings, for $60k and some people will still find something to complain about.
Sure, it would be cool if it weighed less, but at what cost? Should they make the car smaller and lose some interior space? Should they use more lightweight material and push the cost higher? Should they strip the interior to the bare bones and lose the luxury features? It's all about compromise, but with 1.8 kids right now I would have to say that this car is more "livable" than the others, and I can't wait to see this engine in the giant, heavy, 4-door Charger.