This, with a minor difference I'd say.
Sans is the most dangerous not really because of that, but because he breaks the rules. It has been established that he understands the rules of the universe and can bend them (hence the time traveling, fourth wall breaks, teleportation).
In the last fight he doesn't actually deal high damage. As his description says, he is the weakest character: he has 1 damage and 1 HP. However, he bends the rules by hitting a hundred times a second and dodging everything.
That's what I liked about the Sans fight so much. It was a tough fight while staying entirely in character.