Your question is not specific, so I can provide a not-so-specific response which I hope helps.
If you were to have a game that had en equal CPU/GPU usage, then the i3 will reach 100% before the GPU does.
So, yes, your PC will be bottlenecked by the CPU; however as others have mentioned, depending on the game(s) played, and the settings chosen, you can tweak the game settings/graphics settings/resolution to ensure you have equal usage between the CPU/GPU.
I would recommend minimum an i5 Quad Core with a mid-level GPU, such as the 1070 or above.
Still, it isn't a 'bad' set-up per say, and you will not be disappointed with performance, but you will need to upgrade the CPU before needing to upgrade the GPU, hence a more accurate response to your question (I hope)
For 4k gaming, you want to go for an i5 minimum, but be prepared to reduce your graphical settings quite a bit (even with a 1070 GPU) compare to HD or 1440p...