|Not necessarily. If you are using your computer for word processing on a screen with a resolution of 1,080x768 then the GPU is probably not causing a bottleneck in your system. Neither is it if you are using your system as a database server, or as a web server, or if you are running DOS on it (unlikely!). On the other hand, if you are trying to run a flight simulator displaying on 3 monitors each with a resolution of 2,560x1,440 with all detail settings at the highest level, then it's entirely possible that the GPU is throttling your system.|
There are no absolutes to performance; it depends upon the task being done, the operating system, and your requirements. In some sense every component in every system is causing a bottleneck for any application. None of them allow the system to give an instantaneous response. Whether that matters or not is another matter.
Performance bottlenecks can only be determined by doing methodical analysis of recorded performance and then changing one variable at a time to ascertain what difference it makes. Just as there is no best operating system, there is no best GPU. It all depends upon what you want to do.