I too found obtaining the Eidolons to be quite difficult, Bahamut for example, I literally got one second before I would have died from doom. I only really used them if I was being lazy or I noticed I was about to stagger an enemy for burst damage, again Bahamut for example, to do a quick 400k damage. They were boring to use because all you had to do was tap x repeatably as there was no point pressing the buttons yourself. On a last note.. I couldn't even pronounce some of their names!
I prefer them in previous games where they come with a nice little scene, do their attack and disappear until summoned again.