Not one of those guys would have let Gon die in that fight. Hisoka *might* have held back if he judged that between Leorio, Kurapica, and Killua, that Gon was safe. If by some miracle Gon did die, that might have been the end for Hanzo, there'd be no next year. You might reason with Kurapica, maaaaaaaaybe Leorio, but not Killua and Hisoka. This brings me to the underlying point of the whole exam. Gon had next to no chance of actually getting killed. There's exactly one person there who would have been truly willing to kill him (won't say who). No one else taking the exam enjoys this benefit. Beyond that, Gon had next to no chance of actually giving up. This is probably the main reason he ranked so high.