Just throwing my two cents here after playing 10+ games with Koji in various masters. I don't actually think Koji himself is op... outside of a Shenlong crew. Having 3 activations in which you can refill your hand at the cost of 1 chi is a bit ridiculous. Students become way better pass tokens essentially. They bonus to FWP, Concentrate for a chi, and maybe walk if they are too far behind. I would like to see FWP changed to place not Drop.
Outside of the Shenlong draw engine he is 2-4 cards a turn which isn't super broken. And without Shen and the Students moving the markers all over the field, you are very easily leaving points on the table for your opponent. Even in Shenlong you have to be careful about this. For example Set the Trap is gimme points to the opponent.
Leaving enemy scheme markers around can also prove bad depending on the opposing crew. Arson, False Claim, Collette, Linh, Parker, etc. There is a long list of things that love having scheme markers to play with.
Also never put Koji on the table if your opponent declare Crossroads 7. I've never seen models melt so fast in my life.