I think you should consider a few things here, and please remember, that I am a member, avid athlete, and lifter myself, but I'm no university, Ph.D., or exercise physiologist. I'll just share what I know.
First, off, Yes, genetics can play a huge part in how 'big,' someone may get. Bruce Lee, before he became a household name, and martial arts superstar, went through a season of his life where he was convinced that to get to the next level of his physical performance, he would need to get 'big,' and super strong. He started lifting weights, drinking tons of protein shakes, and eating like crazy. However, after trying really hard, and being super disciplined, he was only able to gain a little more weight, and never got 'big' at all. He learned that his genetical makeup, and his somatotype, prevented him from betting 'big.' But, he realized that through the weight training, that he became super strong. He was able to life all kinds of ridiculous weight; it is reported that he could take a Olympic bar, and put a 45lb. plate on both sides (135 lbs.), and hold the bar, with arms extended, straight out in front of him, where his arms were parallel to the floor. He had a specially designed punching bag, that weighed over 300 lbs., and he could be standing beside the bag, motionless, and do a small skip of his feet, and side kick the bag. The force of his kick would like the entire bag off the chains that were holding it, and cause it to fly up and hit the ceiling. He accepted his genetical makeup (meaning he couldn't get "big"), but trained in such a way that he could incredible strong. Chuck Norris once said, that in all the people that he had ever met, 'the strongest person, pound for pound, was Bruce Lee.'
Second, know that a lot of the supplement industry is hype. It is well known that a lot of the these companies, sell stuff that just don't work. However, they work harder at developing aggressive, and deceptive advertising (sometimes, with so-called 'Before & After' photos, that have been photoshopped to make the 'After' picture look drastically improved), than they do at developing, through lots of research, trial and error, and genuine clinical studies (all of which takes A LOT of money/funding, that these private companies do not have, or do not want to spend) authentic products that actually work.
Third, know that a lot of those HUGE bodybuilders did not get 'big' and supercut through the products that they are often seen endorsing, or the usual products that we see on the market, that the average Joe can by in a GNC, or health supplement store. Most of the super huge guys you see, are taking strong, anabolic substances that cause extreme muscle growth; and these 'substances' genuinely work, and work well! This may include testosterone, a whole host of different anabolics, insulin, human growth hormone, and many others that are known to have explosive results. If someone is not using such substances, they will be limited to what their genetic makeup can do. However, it is still possible to create the physique that a lot of men will be envious over, but it takes a lot of discipline, and hard work.
I would recommend, for starters, a book entitled, "Bigger, Leaner, Stronger," by Mike Matthews. I would also encourage you to communicate with 3J, through his site,
3J's Nutrition | Diet and fitness consulting to get you to the next level.. 3J is a nutrition expert, and in his words, it's "80% diet, 15% training"
Hope that helps
