Well now we're at that point in New Waves where Goomoonryong is going to show up again. This is going to be Shi-woon's hardest challenge yet, not only because of the difference in strength but also the fact that he's going to learn the truth behind his master. My favorite part in the final fight of the breaker was when So-chun took on the enraged Goomoonryong because of his experience fighting Shiwoon. He basically became the underdog, which never happened to him before. Then, Shiwoon steps up to the fight based on his master's words... words from his current opponent. I wonder how this is going to change in the new fight if there is one.
Well it's always hard to have the protagonist start off as weak and still get stronger while sticking to his morals without a little boost somewhere. The medicine he took was definitely high-tier stuff, and I'm guessing that's what gave him all that endurance. However, you'd need a strong will to keep getting back up. Just cause somebody has the physical ability to get up doesn't mean they can exceed their breaking point. While this may sound like a cop out, it's vital in fights. Judging from everybody's point of view, even masters wouldn't go as far as Shiwoon would, which means if they were put in his shoes, they would never achieve the things he has.
Now, Goomoonryong did indeed train him and make him part of who he is today. But he was also the one who eventually saw huge potential in Shiwoon. And Shiwoon definitely credits the people who have helped him so far; in fact, the latest chapter has him talk about his willingness to lose limbs for a chance to test himself against true masters. He has a strong motive AND he's got wit to back it up. Remember how Shiwoon instantly caught onto the trick behind foot movements when his sensei demonstrated it? That's credit towards his ability. No random power ups there. Actually, in New Waves he's beaten people in situations where he was crippled due to having no ki center or something similar. He's won a lot of his fights through battle smarts, which makes him a prodigy if you ask me.