The Rolling Rock Canyon was in the Pingst Flatland, a Level 240 to Level 270 map. The next tier would be the last, which will be the Level 270 – Level 300 maps.
Zhang Yang and the majority of his party member had only managed to enter the Level 210 – Level 240 map, yet they were all expected to infiltrate into a Level 240 – Level 270 map. It was either the system wanting the quest to be extremely difficult, or that the system had no intention of allowing players to even finish the quest in the first place.
Naturally, in a higher level map where all the monsters are at a much higher level than you, it would be impossible to escape a tough battle. As such, even if Zhang Yang's party is the strongest party in the entire game, they cannot escape the fate of being killed repeatedly. In fact, at one point, the party was taking turns, dying and reviving.