I'm not sure about how much we know of musculature and fat layers of neanderthals. Working from skeletons of non-humans can be really fraught.
I guess it can be argued that early archaich humans can barely be considered humans, but neanderthals were close enough to sapiens to interbred.
"Species" and "genus" are human (hey-o) concepts that we impose on the natural world to try and understand it, and ultimately this depends on who you ask.