Yes, Sean was not one of the Four Grandmasters in Joy of Life. Although he and Ku He had been ordered to search for the temple together and had practiced the same martial arts secret manual, Ku He had become a Great Grandmaster with his talent, while Xiao En was only a peak ninth-level master. There was a huge gap between them and a Great Grandmaster.

When Sean was young, he was an expert among experts. However, as he grew older, his strength declined. Even though he was the foster father of Northern Qi General Shang Shanhu, he was not stronger than the Four Grandmasters in terms of martial arts. Therefore, according to the information provided, Sean might not be able to defeat the four Grandmasters. However, due to the limited information provided, it was impossible to draw a definite conclusion.
There was no clear comparison between Sean and the four Grandmasters. Xiao En was described as a master of the ninth level. When he was young, he was considered a master among masters, but as he grew older, his strength might have declined. The four grandmasters were considered to be humanoid nuclear weapons and the most powerful figures in the world. However, specifically speaking, the difference in strength between Sean and the four Grandmasters was not mentioned. Therefore, based on the information provided, it was impossible to determine who was more powerful between Sean and the four Grandmasters.
The four Grandmasters were Jin Yong, Gu Long, Liang Yusheng, and Wen Rui An.
The four Grandmasters were the Qing Emperor, Ku He, Ye Liuyun, and Sigu Jian.
The four great masters in Joy of Life were played by Zhang Ruoyun, Wang Qingxiang, Chen Daoming, and Tong Mengshi.
In Sword Snow Stride, there was a ranking of the four grandmasters. Among them, Wang Xianzhi was the undisputed number one in the world, and he was the undisputed Celestial Being Realm on land. Next was Xu Fengnian, the heir of the Prince of Beiliang. He had obtained the Great Yellow Court at Wudang Mountain and the fate of the Demon-slaying Stage at Longhu Mountain. In the battle with Wang Xianzhi in Wudi City, he had comprehended the Celestial Being Realm. The third was Bodhisattva Tuoba. He was the God of War of the Northern Mang. In the army of the Northern Mang, he alone could resist 300,000 cavalrymen of the Northern Liang. Finally, there was Cao Changqing. He was a scholar from the Western Chu Kingdom. His cultivation level was Celestial Phenomenon. During the battle at the Western Fortress Wall, he had fought Xu Fengnian's mother, Wu Su, to a draw.
The four Grandmasters were Situ Xuankong, Monk Chou, Jin Tai, and Zhang Sanfeng.
The rankings of the four Grandmasters were as follows: First was the Qing Emperor, second was Sigu Jian, third was Wu Zhu, and fourth was Ku He.
The four great grandmasters in the << Sword Snow Stride >> were Sword God Li Chungang, Spear Immortal Wang Xiu, Fengdu Green Robe, and Talisman General Red Armor Ye Hongting. Among them, Li Chungang was regarded as the strongest of the four grandmasters. His achievements in the way of the sword were unmatched. Wang Xiu was famous for his cold spear technique and decisive fighting style. Fengdu Green Robe was a mysterious expert, while Ye Hongting was a talisman general in red armor. These four grandmasters played important roles in the novel, displaying their unique martial arts and personalities.
The four Grandmasters of Joy of Life were the Qing Emperor, Ku He, Ye Liuyun, and Sigu Jian. The Qing Emperor was the least powerful but the most decisive grandmaster. He had more of a domineering aura. Ku He was the Imperial Advisor of Northern Qi. He had become the world's first Great Grandmaster through a mysterious secret manual. Ye Liuyun was from Qing Kingdom and had become a Great Grandmaster by practicing Flowing Cloud Free Hand. Sigu Jian was the City Lord of Dongyi. He had become one of the strongest Grandmasters by learning the Sigu Sword Art. These four Grandmasters were all extraordinary experts. Their endings were different. Ku He and Sigu Jian had been seriously injured by the Qing Emperor in the battle at Dong Mountain and eventually passed away. Ye Liuyun had succeeded and left the Qing Kingdom. The Qing Emperor had hidden his strength and eventually revealed his identity.