[narfforc]

I'm not too sure how to interpret mighty in this case. Might doesn't always come in size, being bigger doesn't always mean stronger or better. Ancalagon may have been heavier, more armoured or more intelligent than the other dragons. His fiery or icy blast (if he had one) could have been more potent, of course these things we don't know, along with his size (in which you may be right). What we do know is that he fell from the sky, we don't know how far he fell, weight gains power the faster it moves. The thing that is always overlooked when discussing Earendil, is The Silmaril and Vingilot. This normal ship was hallowed by the Valar, it was filled with a wavering flame , pure and bright, on it sat Earendil with the Light of The Two Trees combined blazing from the Silmaril, nothing Black and Evil could stand up to that for long.