I am late to the party, please forgive me if I repeate something another has already said. I have not found the older threads about the Lamps and origin of the Balrogs...
I think there are not many Balrogs – I believe in Annals of Aman Tolkien wrote that there were no more than 7 of them. I think that Ecthelion and Glorfindel and Gandalf killing one each, with the assistance of a fall into a fountain or off the side of a mountain, and at the cost of sacrificing their own lives, should be emphasized as badass and epic especially because it was unprecedented. Fingon, not at all a pushover, faced a single Balrog in battle and was literally crushed. I think that all but one Balrog would have been destroyed (that is, dis-carnated, reduced to impotent “ghosts”) in the War of Wrath. If Ingwion is to kill one, it should be at the cost of his own life. Eonwë and Thorondor could each kill one. Imagine Thorondor grasping one in his talons and carrying it up to a huge height, while it nearly flays his legs with its fiery whip, and then flinging it down into the deepest unroofed pit of Angband.
I like the idea of Balrogs being essentially faceless and wingless. What should be or was their face is a featureless shadow with eyes of flame. What should be wings are sheets of shadow that look disturbing, but cannot be used to fly. Being reduced to no apparent gender is good, too. I do not think they should be ranged fighters. They fight with fiery swords and fiery whips, and I’ve always thought of the whips as literal tongues of fire that they extrude and wield as whips, not as physical weapons. I do not like mixing in concepts from the Lost Tales, such as an entire race of Balrogs that Morgoth created from scratch. The Lost Tales are so different in character from the Silmarillion and the Lord of the Rings.
I love the idea of the Balrog's own hate and moral corruption finally burning and ruining their fanar, and trapping them in those hideous fanar, at the time they assault and destroy the Lamps. But I'm confused by the reference to Melkor helping to build the Lamps. That seems to contradict the Quenta Silmarillion.
I agree with MithLuin that nobody should kill a Balrog and live to tell of it. And I do not think of Elrond or Elros as warriors. They had to learn to fight, of course, but in the LotR Elrond is a healer. And in Eldarin tradition, healers are not warriors and only go to fight at the last resort. I think being a healer, not a warrior, is a central part of Elrond's character, and probably of Elros' as well. Their part was to try to heal the broken world and people left behind after the War of Wrath.
Sauron and the Balrogs were the mightiest of Morgoth’s demons, but there were other lesser demons, plus the giant spiders of Nan-Dungortheb who were each as terrible as Shelob. Destroying any one of those monsters, or a dragon, is an amazing feat worthy of any warrior. Emeldir may well have had to fight a giant spider or two in Nan Dungortheb or Taur-nu-Fuin to get her people to safety.
(As an aside, I also have finally thought up how Eärendil can kill a dragon while standing on his flying ship. He infuses the light of the Silmaril into a glass arrowhead, similar to the Phial of Galadriel. Then he steers his ship almost into Angalagon’s enormous jaws, shoots him in the eye just seconds before a fire-blast would burn his ship to nothing, then dives his ship out of the way of the dragon’s fall.)