Lower FPS than I think I should have

I had a R7 250 2GB, that could suit just fine @max settings with about 90 FPS but as I dont play only LoL, I wanted an upgrade, and I got myself a GTX 1060 3GB. In every other game that I play now, R6S, CS:GO, Warframe and others there is a big improvement in FPS even with insanely bigger settings (I used to play on very low or low on everything, now running ultra), but in LoL, it will get to 170-180 before I get to lane, then drop to 100 and sit around there, which is like 11%+ performance than my R7 250 could do, like wtf. I even tried lowering the settings to very low, and I was shocked that even on very low, there is no impact. I upscaled the game to 3840x2160 and max settings, there is almost no impact on the FPS. I know there is a possibility of my CPU (FX-8300) bottlenecking the GPU, but I heard LoL is not so CPU dependant, and there is not even a single core running 50%+ only with LoL. The overall processor is in 40% load, I really cant understand what`s going on. And yet, saying that the CPU is bottlenecking, in CS:GO, a game that is CPU dependant, I see huge improvement in frames, I went from 56 fps to 190 in the benchmark at the same settings. Could it really be a bottleneck issue?