Research shows that genetics do impact our ability to build muscle, lose fat, and display athleticism. We all have issues with genetics that we have to work around. Some of us are predisposed to carrying excess fat, some of us are lean but have stubborn areas of fat deposition, some have trouble building muscle, and some are muscular but have weak body parts. Some of us have all of this combined, and nobody has perfect genetics!
We all need to do our own research, tweak the variables, and figure out our optimal programming methodology. Some people respond best to variety, some to volume, some to intensity, some to frequency, and some to density. You have to discover the best stimuli for your body, which will evolve over time.
I've spoken to colleagues about this issue and we're all in agreement: we've never trained any individuals who didn't look better after a couple of months of training, assuming they stick with the program. All of them lose fat and gain some muscular shape. While some lifters have a much easier time than others developing an impressive physique, I've yet to see one train in an intelligent manner and fail to see any results.
So even if you're a "hard gainer" and you don't respond well, you can and will see results as long as you're consistent and as long as you continue to experiment. Of course, the rate and amount of adaptation is highly influenced by genetics, but sound training methods will always account for a large portion of training effects.