I completely agree with you, keeping it simple means keeping mental clutter out when making decisions in the moment. However, can you explain how this (your friend's) system works from step A to Z? If you can, then use it and make a 100:1 win loss ratio. If you can't explain it and its a complete mystery, then how can you learn and apply it?
Also, you said earlier you were looking more into it, so did you find out more what the system is? Can you share with all of us what the basis of his trading is? Naked price action? Ichimokus? SMAs? Even if he was using "gut feeling" there must still be some indication (gurgles, croaks, groaning) when his gut is telling him to get in and out so effectively. No?