What are you implying here? Do you never go to failure with heavy weight? If so, you're missing out on some great size gains! I think you might need to re-think your training. Trying to beat the log book works! Maybe not every session, but just going into the gym and pumping away on many exercises and hoping you get stronger someday sounds far from optimal! For example, I can't beat the log the log book every week like I used to, so I have to use different periodization in my training, but I still go by the book to plan for an all out max day pushing heavier weights than before. Using low rep ranges with 80+% of one's max is also key to getting progressively bigger and stronger.
Also, everyone is going to reach a point where doing the same thing isn't going to work forever, so one must try new methods. Mark is huge and I am sure very close to his genetic max, so I'm sure he has to be creative in his methods, thus, prob why he hired JM. JM knows his crap and trains a lot of people. Plus, JM is prob good at keeping injuries to a minimum.
As for powerlifters, most of the 200+ pound guys have muscle, but I agree they could be bigger based on the weights they use, but they do not train in the optimal rep ranges for size. Most only train above 10 reps for a few weeks at limited times. They also are using leverage techniques and very low reps 90% of the time.