My dad had a saying, I think it applies here: "A poor workman blames his tools"
Ehh...yes and no. A workman generally isn't competing against others, which is why he has no excuse. Not so with gamers.
If two craftsman are up against each other in a woodworking competition, their tools absolutely matter. Give one a dull blade to work with instead of the sharp one the other guy has, and he'd have every reason to complain about his tools and how they're affecting his ability to produce results. After all, the fact that he is fully capable of producing absolutely amazing results using just that dull blade doesn't matter one bit in a competition setting, since what matters in a competition is his ability to produce better results than the person he is competing against.
So it is with much of gaming.
A "craftsman" of the gaming world may be more than capable of producing amazing results on an everyday basis by wiping the floor with their opponents, regardless of their tools, but put them up against someone of similarly-masterful skill and their tools can absolutely make a load of difference.
That said, I actually agree with your sentiment, since computers, latency, and other factors get overused as excuses when the bigger issue is merely the player's competency. I recall back when I played vanilla World of Warcraft, I was getting 0.5 frames per second (i.e. 1 frame every two seconds; that is not a typo) at minimum settings in some of the raids, simply because I was at the time running the game on a laptop that was well under the minimum specs (the bug tunnel in AQ40 was particularly bad for me). Yet, despite that, I'd consistently come in with the least "overheal" and the second highest healing among the members of the 40-man raid (i.e. I healed the second most and did so with better efficiency than anyone else). When the raid leaders got wind of how poor my computer was, they started calling the other healers to task over their performances, since if I was able to produce those sorts of results with such a crappy setup, the others had no excuse.
All of which is to say, bad gamers do indeed blame their tools inappropriately in the vast majority of cases, but gamers also have better and more valid reasons for blaming their tools than a typical craftsman.