: Didn't you read the prophesy of Mandos.
: They didn't diminish of age alone, but in ME they did diminish.
: In aman they didn't. What you resd meant that they didn't get old
: and diminish with old age, which is correct. But after a time the elves, especially Eldar, didn't have place in ME so they diminshed, even as individuals.

Yes, that is how I read that statement too.
That they did not diminish with age simply meant that old age played no part in an elf's decline. BUT, the overall effectivenss of elven kind, and the new off spring were getting progressively weaker. They're "Magic", or whatever made them powerful, and different from men was waning.

Basically, elves were waning, not just due to decline in numbers.

Again, look at third age elves, compared to first agers.
Don't look at Galadriel, because she is a First Ager. Just because she lived that long does not mean anything. What we're comparing here, are elves born in the first age, who may or may not have seen the light before the sun, and third agers, such as Legolas. There is simply no comparison. Third Age elves such as Elladan and Elrohir (okai, okai, they're half elven, but they chose to be of elven kind, and anyway the maia blood should INCREASE their potency) are OBVIOUSLY not as hardy as First Agers, such as Fingon ad nauseum.

The actual power of Elrond is debatable, but I don't think he could face a Balrog, and he certainly couldn't face Sauron during the war of the Ring.

Given a First Ager, such as Fingolfin, I think he would have been able to withstand Sauron in single combat, but no Third Ager would.

Simple as that.

Gandalf