Leon would rather trust the devils, who are lawful evil, than believe in the treacherous and unreliable Yugros Demons who are neutral evil and could betray at any moment.
Those creatures are simply too unreliable; a wise man doesn't stand under a crumbling wall. Though with a contract in place, there's less need to worry about tricks from a Yugros Demon.
Leon burned an Ophalos Demon to death with a burst of Samadhi True Fire. He deliberately checked afterward, confirming that the creature hadn't liquefied into a puddle but had indeed left behind only some ashes... Honestly, he couldn't guarantee that he'd completely eliminated it in the Material Plane, thwarting its rebirth in the Burning Flame Hell.
Hunting Demons fear the Samadhi True Fire, and Ophalos Demons do too. Clearly, the fire can threaten them, but the extent of its threat remains uncertain.
