But how do you know that there is more muscle? You only know that there is more mass based on the premise.
My point is that muscle cells across animals don't have significantly differing density. However, different individuals (of any species) may have different levels of glycogen and fat embedded in the muscle, which may contribute to your point of "muscle density". It is just a loser terminology of muscle density as such. Even then, I doubt that muscles mass for the same volume of muscle could change that much across individuals.
All in all, I am just arguing for more specificity in your hypothesis, because I think in its current form, it isn't adding much clear detail.
