Gardener, you pose some good questions.
Clearly, Sauron's forces in the Second Age were overwhelming, at least until the Numenoreans came into the picture. Then Numenor's overwhelming force outweighed Sauron's overwhelming force regardless of the Ring. Even after Numenor fell, the West was able to scrape together sufficient force to defeat Sauron, again with the Ring.
To repeat comments from an earlier thread, found here
http://forum.barrowdowns.com/showthread.php?t=19065, JRRT says in Letter 131 that the One "contained the powers of all the others, and controlled them, so its wearer could see the thoughts of all those that used the lesser rings, could govern all that they did, and in the end could utterly enslave them." But the Elves simply took off their Rings, so, other than perhaps control over the Ringwraiths (it seems that the One did not effectively control the Dwarves that wore the Seven), the effect of the Ring was really minimal during the wars of the Second Age.
In contrast, during the Third Age, Rivendell and Lorien may have relied heavily upon the power of the Elven Rings to establish and maintain those realms and if Sauron recovered the One, his force would have been enough to defeat Men with the Elves diminished due to the loss of the powers or Sauron's control of their Rings.