Why didn't the Eagles help out more with the destruction of the Ring - once Gandalf knew what was going on and Gwaihir had saved him from Isengard, Gandalf could've asked him to attend the Council of Elrond and once the decision had been made the Eagles could have flown the Ring all the way to Mount Doom and done away with it? - It would've made things so much easier...
I believe this has already been discussed elsewhere. I remember posting about this matter maybe two or three years ago.
They didn't do that because they weren't allowed by the Valar. It was up to the Free Peoples of Middle-earth to overcome Sauron. Whilst the Istari were sent merely as Guides, the Eagles served another task, as messengers of the Valar.
Direct intervention by the servants of the Valar in Middle-earth was strictly prohibited; this is true for both Istari and Eagles, safe on a few occasions where they were told to act by Manwe - for example Gandalf being lifted from Orthanc, Gandalf being dragged to Lothlorien after his rebirth, the Eagles countering the Nazgul and saving the Hobbitses after the downfall of, Sauron.
From a more practical point of view, there would be hardly any story left if the Eagle Express did all the labour.
From a more cynical point of view, why let the Eagles do all the work if you can make the Free Peoples of Middle-earth suffer terribly?
Yes, a good ordeal is necessary to keep the Peoples fit and on their toes, it stimulates the physical and mental prowess... it's the essence from which heroes and heroines are born. If Arda hadn't been the purgatory it had become, but instead had been a paradise since the beginning, its peoples would've merely changed into an equivalent of H.G. Wells' eloi
that appear in The Time Machine
: numb, stupid -but happy- walking husks, preyed upon by Morlocks (Morlorcs?), and living empty, useless lives deprived of any excitement whatsoever, filled only with eating, drinking, dancing and lumbering around.
(Why, Hobbits are actually very alike to eloi
Hence indeed, one should thank the evil powers, for without them there would be no Silmarillion, no LOTR, no heroes and heroines, just boring, unexciting bliss of happiness... and who would want that, eh?
Give up the Halfring, she-elf...