Yes genetics!! Do you not understand that genetics determines everything. You will only get so big due to GENETICS. The peaks are determined by GENETICS. The chest split is determined by GENETICS. Do we really need to explain this to you or anyone who is even remotely familiar with bodybuilding?. Everyone can improve no matter what. So yes benches may not make your chest grow but flys might. That by itself doesnt mean GENETICS. that just means your body doesnt grow from benches. Maybe your doing it wrong maybe to heavy maybe not heavy enough etc. Thats not genetics. How big and developed you become is GENETICS.
There are better and worse exercises and better and worse ways to do them but do you really think someone who could not make their chest grow at all with barbell benches suddenly will make it grow with flies?
Why is this scenario unlikely? Because the barbell bench will hit chest no matter what in anyone, there is no way to do it without engaging the pectorals. Yes some may feel it isn't optimal for their structure and hurts their shoulders or whatever, but my point still stands. Therefore I say that genetics is the prime factor in development, not exercise selection. Genetics as in having enough fibers to work with.
Another example would be quads. If the genetics for good quads are there, both squats and leg presses will hypertrophy them. Squats may hurt a guys hips or lower back but it's not like the squats won't grow the quads at all whereas they suddenly explode with growth on leg presses.
Any number of exercises that hit the area will work. Some a little better, some a little worse but the exercise selection is somewhat secondary.
