You seem awfully passionate about excluding anything but midsize performance cars from the blanket term "Muscle Car". Why is that? Respectfully, I'm just genuinely curious about your opinion, and maybe I'll learn something new today.
Because I was around, and paying attention, in the late 1960s and 1970s. Back then, there was no homogeneous Performance car market like there is today. Back then, cars were designed, produced, and marketed to very specific and well defined market segments.
The Sports car was defined by two-seat, small, great handling cars. They were not designed for power/speed, which is why sports car racing has always been more about road courses and handling tests than speed and they never went to NASCAR.
The 1964 1/2 Mustang was a Compact car that created a new market based on styling that came to be known as Pony cars. After that, any compact with a long front/short rear deck (Camaros, Firebirds, AMX, E-bodies, etc.) was marketed as a Pony car. Ford viewed the Mustang as a four-seat Sports car, and directed its marketing efforts towards Sports car owners. This is why Mustangs, and other Pony cars, were designed and built to meet Sports car racing standards and given names to reflect that such as Trans Am (both the Pontiac and the Challenger T/A).
The Muscle car market started in 1964 when Pontiac decided to offer a plain midsize coupe with increased performance and everyone else followed suit. The Tempest became the GTO, the Satellite/Belvedere became the GTX and Roadrunner, the Fairlane became the Torino, etc. These were marketed as go-fast cars and found their support from racing venues that appreciated speed over handling, which is why our cars ended up in NASCAR and not any other sports car events.
Plymouth and Dodge had midsize production rolled into fullsize, and didn't break it out as a separate business unit until 1965, mainly as a result of the success of GTO sales at Pontiac, and at that point they had Compact (A Body), Fullsize (C Body), and now Midsize (B Body) divisions, so there was never a homogeneous Muscle Car division that cranked out high-performance A/C/B bodies. Muscle cars were under the Midsize division only, and the focus of the Compact performance group was on the Sports and Pony car markets. So from a production and buyer perspective, Sports, Pony/Compact, Midsize/Muscle, and Fullsize cars had very unique and differentiated production and markets.
Now jump ahead to the 1980s, and after decades of Sports and Pony cars being the focus of attention, we now have Muscle cars getting noticed and more and more the terms Sports and Pony sound either snobbish or girly, and we saw the start of efforts to redefine Muscle cars as pretty much any old car with a big engine in it, be it a Compact, Pony, Sports, Fullsize, or whatever, even if it was made ten years before the Muscle car market was even formed. Sports and Pony became uncool, Muscle became cool, and everyone wants to be cool, so we have people wanting to apply the term nowadays to pretty much any old car even if it's a /6 Duster.
