Keep in mind with Gwaihir - if you are dealing damage when they enter play, it means the enemies weren't killed last round and already made their attacks. If you are dealing damage when they leave play, it means that you are losing an ally on the table.
How much direct damage you you sustain with the eagles like this? Maybe 2-3 damage per round? I think Thalin, Ranger Bows, Expecting Mischief, and other direct damage effects are on the same level. And some of those effects are better because they don't happen during planning.
Gwaihir would also make Descendant of Thorondor into a great Sneak Attack ally. The only thing better would be to sneak attack in Gwaihir ally and bring in Descendant from the discard pile, but you can't do that with the hero in play
.