as your very first statement "all things being equal". They're not. Around athletes, those heavier guys (i.e. linemen) are used to moving around that extra weight all the time.

Running, jumping, lifting etc. As such there core strength, and strength in general would be higher.

Of course for someone from the general populace who would know the difference between a proper squat and a deep knee crick, I could see validity in calling it a disadvantage.

Just a different way of viewing it than I do.