Basically I say they are the same even with those differences, as the differences are slight. I guess the most glaring difference with the Charger and RoadRunner is the wheel base or rather the ass end of the Roadrunner is longer, but to me that is a difference without a distinction.
I tend to agree with you. I always called the Camaro and Firebird the same car. They had unique sheet metal for a bit like the Mopar cars we were speaking about, yet unlike the Mopars, their drive trains were different by brand.