I could be wrong on this but I believe it goes something like this...
Type I Fibers are Red, Slow Twitch Fibers. This is the endurance stuff.
Type IIa Fibers are Red, Fast Twitch Fibers. This is the fiber type that you can make nice and big.
Type IIb Fibers are White, Fast Twitch Fibers. It sounds like the thinker is saying there's not a lot of room for improvement with this fiber type.
Type IIa Red Fibers are very trainable. Between training these fibers through lifting in the 5-15RM range and training the CNS through lifting in the 1-5RM range you can get big and strong.
So if genetic limitations are mainly on white fibers, then healthy individuals are capable of gaining considerable amounts of muscle mass by training Type IIa Red fibers.
An Aspiring Powerlifter whose genetics have left him with less-than-world-class Type IIb fibers will need to accept the fact that he will not be able to get an elite total at his current bodyweight of 165 and height of 5'9".
So between training his Type IIa Red Fibers and his CNS with heavy weights, he can still reach his lifelong goal of an elite total by putting on enough muscle to walk around at 250lbs and compete at 242.
Maybe I'm wrong. But if I'm wrong then I just don't get the whole picture. It's not because what the thinker says is wrong.
Maybe I'm biased - but the argument that type IIb fibers aren't very trainable just makes a lot of sense.
I attempted to throw Javlin last spring and I was TERRIBLE. Despite the fact that I was nearly twice as strong as everyone else throwing Javlin my distances sucked huge donkey balls.
(Although this had a lot to do with my novice level technique, much weaker kids with technique about as bad as mine could still throw farther than me.)
I can out Power-Clean everyone I knew in High-School who can Dunk, but I'm not even close to being able to Dunk.
Well, then how is it that the Olympic Lifts and Dynamic Effort Power Lifts can be done so fast with such heavy weights by the big, strong guys? I'm assuming that explosively Benching 275 has a LOT more to do with Maximal Strength, Type IIa Red Fibers, and CNS efficiency than it does Type IIb fibers.
ALL OF WHAT I"VE SUGGESTED IS A GUESS