[Kuruharan]

Because Feanor was a spoiled brat, the entire family was doomed. I don't know...but that sounds a wee bit unforgiving to me.

No. The entire family was “doomed” because they followed him of their own free will (except for Finarfin who turned back).

the sorrow of Maedhros and his brother Maglor

I’m not certain that the suffering of those two children of their father really counts for much. Actions matter.

On top of all that, they put a stipulation that one must come pleading for both elves and men -- and even then it was only a might.

Literary convention.

Even through all the bloodshed…the death of all the brave and noble men of Middle Earth

Here is a part of your argument that I don’t understand. There was plenty of slaughter in the War of the Ring, but you seem to feel that it was more eucatastrophic.

I believe you feel this way because the LOTR focused more personally on specific characters. If you read the account of the exact same thing in “Of the Rings of Power and the Third Age,” you probably don’t get that same feeling of eucatastrophe that you do from reading LOTR. This is because the style is different.

After everything they're not full of pity...

They’d been grossly offended, something the defenders of Feanor tend to gloss over.

Emphasis mine of course. Earendil who wanted to plead his case wasn't even allowed to come near the Valinor -- it's almost as if the Valar didn't even want to be moved to pity unles that one had a Silmaril.

That is what makes it eucatastrophic. Earendil overcame greater odds than Frodo because Earendil was contending with a greater force.

they are bound by their oath, and they don't know who can release them.

It's not even said here that the sons of Feanor were forgiven. They were merely told to give up the Silmarils and to wait for judgement. That does not sound like forgiveness, and they were both sorrowful for their oath. They did not want the Silmarils for their beauty, they wanted the Silmarils to fulfill their oath.

Their oath was wrong. They should have chosen to accept their disgrace. If they really were past the point of saving themselves, they could have worked to help others and have caused less damage.

The end of the Silmarillion is victorious. However, it is tainted with sorrow, with the foolishness of the Valar, with the folly of Feanor, and the sorrow of the unforgiven sons Maedhros and Maglor. It is not a Eucatastrophe.

The end of The Lord of the Rings is also victorious and tainted with sorrow, with the failing of the elves and dwarves, the inability of Frodo to be healed, and the continued diminishing of the Dunedain since Elessar was their last great flowering. Why is this a eucatastrophe and the Sil not?

Again, I think the answer lies in the style of the respective works.