the MC wasn't kicked out of his clan or anything, he just left. He transferred because he claims he 'has no talent' and yet we find out later that he won every competition in his age group and has a vast store of practical knowledge, skills, and experience despite that 'lack of talent.'

as the story moves along the magic seems to take on aspects of spiritual cultivation while the fighters are more like body cultivators, the only difference is they use mana instead of Qi. So his 'lack of talent' has more to do with his difficulties circulating mana the way a fighter needs to use it and despite that 'lack of talent, ' he was still the guy winning all the competitions. I could only wish I could be even close to as 'untalented' as he is at the start of the story.

if he s**ked at fighting and continuously failed challenges despite working hard, I would understand him giving up and moving on to something else, but it wasn't like that at all. He never failed at anything. He was always the champion and the fighter who came out on top, the pride of his clan and the person everyone looked up to. It's not a case of him pretending to be better than he is; he has bad-ass fighting skills, which we see some of in the way he handles those bullies in the other reality. Perhaps his 'lack of talent' will be explored later in the story; the author brings it up at least once a chapter so I hope he gets on with it sooner rather than later.

because there was no single moment (that we're aware of so far) where he failed as a fighter and nothing that triggered a need for change his sudden switch seems more like whim. As though he hit a wall (or got bored) and rather than trying to push through it he decided to give up and do something else because it was easier than working hard. It's backwards from the usual Korean trope of 'hard work can accomplish everything' but OK.

he's also presented in the summery as a loser, but he with all of his elite training and experience, there's no way he ever possesses that mentality, even at his lowest point.