Just to point some things out, Gnome is also able to warm Jee-Han of danger, and has done so multiple times in the past. This would also add to his forms of precognition.
To clarify on the Gamer's mind, it essentially keeps him calm and prevents him from going insane where a normal human would. It has some ability to ward outside mental influences as the only one able to get inside his head thus far was someone who was a kind of pseudo god within their verse, but his mind has never been tested against such extreme mind hax. However, as his mind will constantly remain calm, and he will constantly have little screens popping up warning him of Sasuke's intentions, then it can be argued that Sasuke's genjutsu is a bit of a mute point here.
Thirdly, as far as hand to hand combat goes, Jee-Han is far less experienced when compared to Sasuke, yet he has had some training in the martial arts, and specifically trained enough to boost his body to defend himself, such that he can provide himself with time to take to the air. In the second to most recent chapter, he can be seen shattering a barrier with just his foot alone (this barrier took multiple city block to multi-city block level attacks from someone who is somewhat wearker than him). So his physical attacks actually do cause some decent amount of damage. But, as said earlier, he literally learned marital arts to help him with his job of being a magician, such that he can manuever around more skilled fighters, and take to the air where he has an immense advantage. He's done this against his best friend whose been training in the martial arts for likely a decade, so it certainly does work.
