[Urwen]

The Fall of Gondolin was written by survivors of Gondolin and later by Bilbo. Are you saying that the survivors of Gondolin weren't biased?

That goes especially for the teller of the original, Littleheart, son of Bronweg. Bronweg was close to Tuor, who killed Maeglin. Bronweg was one of biased ones (against Lomion) as a result, and he told the biased version to his son. Like the part where Meglin had Orc's blood in his veins. Bronweg and many other Golodhrim hated him, and so had an aptitude to write such a story where all the blame would fall squarely on his shoulders.