Of Eorl: The line thought broken

[Inziladun]

The golden-haired tendency of the Rohirrim could indeed be explained by a connection with the House of Hador, but at further removes from Tuor specifically.

The Northmen of Rhovanion eventually became the Rohirrim, and of them it is said:

[They] were descendants of the same race of Men as those who in the First Age passed into the West of Middle-earth and became the Allies of the Eldar in their wars with Morgoth.

Unfinished Tales Cirion and Eorl

Footnote Four adds:

The Northmen appear to have been most nearly akin to the third and greatest of the peoples of the Elf-friends, ruled by the House of Hador.

The genetics for blonde hair were simply present in both some of the Edain who went into Beleriand and their kin who remained behind.