Thrice shall pay for... what?

[Raynor]

Nevertheless, you're probably right about Gwaihir not being the 'king' of the Eagles. Whenever he's mentioned, it always seems to be in the terms of his being the 'swiftest', or having 'far-seeing eyes', and you'd think if he was the ruler of the Eagles that fact would be somewhere noted.

Well the eagles are names as vassals of Gwaihir and Landroval, however only Gwaihir bears the name "the Windlord"; considering the nature of this race, this title should establish his prominence among all the other eagles - I am not quite sure we can imagine another title surpassing it in significance.