Honestly, I think the dominance comes from a combination of raw, elemental threat and a surprising degree of narrative flexibility. They're not just big lizards; they're often embodiments of catastrophe, a force of nature with a malevolent intellect. That creates instant, high-stakes conflict. An army is a logistical problem. A devil dragon is an existential one. It reshapes the geography, the politics, the very magic system of a world just by existing.
But the real hook for me is the moral ambiguity you can layer onto them. A classic dragon might just hoard gold. A devil dragon might hoard souls, or memories, or time itself, forcing characters to question what they're willing to sacrifice. Look at the deep lore in something like 'The Priory of the Orange Tree'—the dragons there are integral to the world's balance, neither purely good nor evil, which makes the conflict so much richer than a simple slaying quest.
Plus, let's be real, they're a fantastic vehicle for exploring power dynamics. The relationship between a rider and a devil dragon, or a sorcerer trying to bind one, is instantly charged with themes of domination, submission, partnership, and corruption. It's a power fantasy with built-in consequences, which is catnip for a certain kind of reader. You get the thrill of immense power, but the story automatically asks if you can handle it without losing yourself. That tension is everywhere in the genre right now.