Yes, a new GPU will be bottlenecked by your CPU. But at the same time if you have a good motherboard that can handle a better card, you can easily double your performance in gaming with a 1060 (probably even a higher card works but you won't need that much juice yet, 1070 max recommended). And you can hold that GPU for later upgrade also.
A quick youtube search shows that you can easily get double the fps on games like Witcher 3 WITH YOUR 4300 FX. So honestly the first and fastest upgrade you can do (even bottlenecked) is to upgrade your GPU. Maybe even OC your CPU a little since you'll be changing it in the future also. https://www.youtube.com/watch?v=RmmMTjGuWRU