Actually, where the bottleneck is varies by the game.
Some games need a lot of CPU. For example, Starcraft 2 would be limited by your CPU most of the time. A game like Tomb Raider is probably more limited by the GPU (not that it's playable).
Also, the i3-530 only has TWO cores with hyperthreading (2C/4T) and relatively weak cores at that, so WINDOWS is going to probably eat a lot of that, especially when a demanding background task suddenly does something.
So NO, it's a big stretch to simply say a GT730 would be the bottleneck. Just not true in many (most?) situations.
So...
Again it VARIES but for very light gaming I'd get at least a GTX730.
BTW, there are different models of GT730. Some have more CUDA cores than others. Some only have 96, and some have 384 so there's a HUGE DIFFERENCE between those.
Also, I would get a GT1030 instead (unless you need a VGA output). It's a better card for a similar price (new).
https://www.youtube.com/watch?v=fXCSG6zdxdQ
https://pcpartpicker.com/product/8h648d/evga-geforce-gt-1030-2gb-lp-video-card-02g-p4-6332-kr
Make sure your MONITOR connection is supported (some are DVI + HDMI, and some are DVI + DP) so if you need HDMI make sure the card you choose has HDMI output.