A Balrog's weakness isn't a simple vulnerability but lies in being overcome by superior power, especially divine or "Secret Fire," and its own fiery nature, which water can dampen, though its immense strength makes it incredibly hard to defeat, requiring a powerful foe like Gandalf or Glorfindel.
Balrogs have no particular weaknesses to light or any magic really, as they are supremely powerful in magic themselves, which is why every Balrog that has been killed was killed by arms or force, not magic.
Gandalf pursued the monster for eight days, until they climbed to the peak of Zirakzigil, where the Balrog was forced to turn and fight, its body erupting into new flame. Here they fought for two days and nights. In the end, the Balrog was defeated and cast down, breaking the mountainside where it fell "in ruin".
Gandalf was not in his full Maia power. He (and the other Istari) were reduced, even incarnate, while the Balrog presumably had full strength.
Maiar vary greatly in abilities, and therefore power. Balrogs are physically stronger than Sauron but Sauron has greater magical ability and intellect. And those would go a long way overall in handling any Balrog.
In the books, Legolas actually screamed in terror when he realized that a Balrog was coming. It was the Balrogs that rounded up the elves for Morgoth, to be corrupted into orcs.
The Balrog wins. Smaug is devastating in the mortal realm, but the Balrog is essentially a god tier being masquerading in flesh. Unless Smaug killed the body and had some way of banishing/destroying the spirit, the Balrog would eventually triumph though it would be one hell of a battle. Both are rare and elite.
Why was Sauron afraid of Aragorn potentially possessing the Ring? Gandalf explains it in the Return of the King (during the council after the battle of the Pelennor fields) that Sauron would never think somebody would want to destroy the One Ring.
The “wings” referred to earlier in the LoTR text were merely the darkness (aka “the shadow”) with which the Balrog surrounded itself taking on a great, terrifying shape; there is no suggestion in the text that the wings were physical in any way or required for any of the balrog's actions (other than its attempt to ...
Tolkien's description of Gollum conforms to a Catholic – and Thomistic – account of envy, which is a “sadness of the soul”; and it is Gollum's unbearable sadness and his unquenchable desire for the one Ring that marks his character.
In Tolkien's later writings, he noted that there were no more than three or seven Balrogs. In an early draft, there was a Lord of Balrogs named Lungorthin.
As a Maia, Gandalf was an angelic being in human form, in service to the Creator (Eru Ilúvatar) and the Creator's 'Secret Fire'. He took on the specific form of an old man as a sign of his humility. His role was to advise but never to attempt to match Sauron's strength.
But at the Council of Elrond, Gandalf very specifically says he fought all nine. He drew four of them off when he fled northward at dawn; "This helped, a little, for there were only five, not nine, when your camp was attacked."
Ecthelion killed three Balrogs and his sword did "hurt to their fire". However, dragons reinforced Melko's army.
Balrogs have significantly more spiritual “power” than dragons. However it seems Tolkien made exceptions for special characters like Smaug and Glaurung, who were especially intelligent, capable of speeches and spells, and thus all the more villainous. But on the whole, Balrogs > Dragons in the order of being and power.
Gandalf is probably the strongest, he did defeat the Balrog or Durin's Bane. The evil ones squandered much of their native power in lust for dominion and evil.
He was travelling and being a good old wizard chap. Pretty much the only notable event is him poking in Dol Guldur when Sauron first came to reside there.
Frodo left Middle-earth due to lasting injuries from his journey, seeking healing in the Undying Lands. His decision was influenced by trauma and a desire for peace, similar to Tolkien's own experiences. In Rings of Power, Frodo is portrayed as a hero who found solace and closure in the Undying Lands.
Saruman first appeared during a fourth phase of writing in a rough narrative outline dated August 1940. Intended to account for Gandalf's absence, it describes how a wizard titled "Saramond the White" or "Saramund the Grey", who has fallen under the influence of Sauron, lures Gandalf to his stronghold and traps him.
Elrond chose the fate of the Elves and therefore the choice was presented to his children. The reason why Eldarion and his sisters (the children of Aragorn and Arwen) were born mortal was because Arwen chose mortality and therefore that fate was passed on to the rest of their line.
He was terrified in a way beyond comprehension. Gollum knew if Sauron ever got it back, he would never possess it again. Gollum/Smeagol was a twisted and tragic character, but, like the other characters, he too was facing fear, internal conflict, and risking his life to stop Sauron from getting The Ring.
Q: Who would win in a fight, Tom Bombadil or a Balrog? Bombadil, easily. Remember that the Ring held absolutely zero power over him. Tom would not fight a Balrog.
Well, there's also a hierarchy of power within the Maiar as well -- Saruman is more powerful than Gandalf, by his own admission, and Sauron is maybe the strongest of all the Maiar, being the chief lieutenant of Morgoth himself.
He fled there are the breaking of Thangorodrim, but was followed by an elf-maiden Glathlírel who was determined to end him. The Balrog eluded her for millennia, until she was able to face him in combat and defeat him.