Also completely untrue. Glenn Dorsey was like 275lbs. Tony Whites DL at Syracuse 4 of the top 5 DL were under 285lbs.... In the simplest way I can describe it, it essentially depends if you are running a 2 gap technique up front, or a gap-out technique. Not saying those are official terminology, but for description. If your front is controlling 2 gaps, its much more dependant on being stout and holding the point of attack, so A: those gaps are open(no free blockers) for your linebackers to fill and make plays B: your DL can react and make a play to either gap.
In a gap out or attacking style scheme, which is what Tony White ran, and Michigan under Don Brown, etc. Where the defensive call dictates which defender attacks which gap on a certain play. Essentially you have guys attacking all of the gaps. This is why Tony Whites defense produced so many TFLs, because you have guys penetrating and creating havoc in their gap or behind the LOS. The con can be if your calls are off and slanting or attacking wrong gaps, or if you pentrate beyond the play it can lead to gash plays from the offense.
All give and take. All Come down to fit, scheme, and play caller.