Thoros of Myr: Underrated Fighter (Spoilers Extended)

Background

Recently, I Ranted In Support of the Skill of Ser Loras Tyrell. Here I am again to rant in support of Thoros of Myr.

I will state that I don't think Thoros is the best fighter, just underrated, while also noting that GRRM stated:

GRRM: I get fans who ask me, "Who is the best warrior, or who would win in a sword fight between this character or this character?" My answer is always is that it depends on the day. You have to use sports as an analogy. Yes, you can say Johnny Unitas was a great quarterback but it doesn't mean he won every time. He lost some games. The greatest boxers lost occasionally. Even Man o' War was defeated once in a horse race. So we can rank these swordsman and we can rank the knights and we can say who is good or who is bad but still an upset is possible. Of course with knights, if you get upset, you may die or have a limb hacked off. They are playing a sport that is very dangerous. -SSM, SI.com Podcast: 6 Mar 2013

Skill in Melees

Thoros wins the Melee during the Tourney of the Hand:

The melee went on for three hours. Near forty men took part, freeriders and hedge knights and new-made squires in search of a reputation. They fought with blunted weapons in a chaos of mud and blood, small troops fighting together and then turning on each other as alliances formed and fractured, until only one man was left standing. The victor was the red priest, Thoros of Myr, a madman who shaved his head and fought with a flaming sword. He had won melees before; the fire sword frightened the mounts of the other riders, and nothing frightened Thoros. The final tally was three broken limbs, a shattered collarbone, a dozen smashed fingers, two horses that had to be put down, and more cuts, sprains, and bruises than anyone cared to count. Ned was desperately pleased that Robert had not taken part. -AGOT, Eddard VII

If interested: The Hand's Tourney: The "Winners'" Gold & the Brotherhood w/o Banners

and:

The shifting flames painted Sandor Clegane's burned face with orange shadows, so he looked even more terrible than he did in daylight. When he pulled at the rope that bound his wrists, flakes of dry blood fell off. The Hound's mouth twitched. "I know you," he said to Thoros.

"You did. In mêlées, you'd curse my flaming sword, though thrice I overthrew you with it." -ASOS, Arya VI

The Walls of Pyke

We find out that Thoros was the first one through the breach when Robert brought down the walls of Pyke during Balon's First Rebellion:

The girls giggled over the warrior priest Thoros of Myr, with his flapping red robes and shaven head, until the septa told them that he had once scaled the walls of Pyke with a flaming sword in hand. -AGOT, Sansa II

and:

Ser Jorah nodded. "By then my father had taken the black, so I was Lord of Bear Island in my own right. I had no lack of marriage offers, but before I could reach a decision Lord Balon Greyjoy rose in rebellion against the Usurper, and Ned Stark called his banners to help his friend Robert. The final battle was on Pyke. When Robert's stonethrowers opened a breach in King Balon's wall, a priest from Myr was the first man through, but I was not far behind. For that I won my knighthood. -ACOK, Daenerys I

and:

"I was talking about Thoros." Gendry reached out with the tongs as if to pinch her face, but Arya swatted them away. "He liked feasts and tourneys, that was why King Robert was so fond of him. And this Thoros was brave. When the walls of Pyke crashed down, he was the first through the breach. He fought with one of his flaming swords, setting ironmen afire with every slash." -ASOS, Arya IV

The Battle of the Burning Septry

 Thoros and Lord Beric were everywhere, their swords swirling fire. The red priest hacked at a hide shield until it flew to pieces, while his horse kicked the man in the face. A Dothraki screamed and charged the lightning lord, and the flaming sword leapt out to meet his arakh. The blades kissed and spun and kissed again. Then the Dothraki's hair was ablaze, and a moment later he was dead. She spied Ned too, fighting at the lightning lord's side. It's not fair, he's only a little older than me, they should have let me fight. -ASOS, Arya VII

If interested: A Man Meeting His God: Thoros and R'hllor
TLDR: Thoros of Myr is not be the best fighter ever. But he is extremely underrated/fearless and probably lives in the nightmares of numerous Ironborn.