"It's okay," Pirren said when Jin finished showing his performance. "Your current limit is 20 moves, and that's only when performed slowly. But that's very good for just one month of training." He seemed pleased on the outside but was quite surprised internally.
Without a teacher or mentor, not even someone to help him understand difficult concepts, Jin reached this level. He was probably busy with the recent Starhold inheritance war and didn't devote all his time to the MorningStar Sword.
But now, with 100% focus on the martial art and a master like Pirren, who has perfected the art, Jin would progress rapidly. He could become a talent that elevates humanity and eradicates or enslaves other creatures forever.
Despite using a demonic body—a fact Pirren detested—he admired using the enemy's power against them. Plus, Jin's mind and spirit were human.