Is there a problem with GeForce 750M performance on gaming?
Intel is making big improvements in the Integrated Graphics performances.

They are actually taking a portion of the Nvida market in doing that.

To Intel, the Nvidia is just a parasite, so if they can do better with the iGPU performance, ppl wont need it.

Intel will be introducing next gen CPU with some powerful iGPU in 2015.

There is no official benchmarking for the Iris Pro vs G750 but as usual the performance is highly game type dependent.

As you have discovered for the League of Legends it looks like the Iris is actually doing better then G750.

There are some games where the G750 is doing better, like Startcraf2 and Heaven.

see this report for more.