[Tuor of Gondolin]

While Feanor had virtues, in temperament he and Maedhros bear
comparison to Sonny Corleone ("you can't do business with
that hothead") and his brother Michael.

An Elder/Edain alliance, however, without the Curse of Mandos
and led by Maedhros, would not only be united
and,of course, not cursed (duh!) but would have a maia of their
own as an ally with the same haven of Menegroth to rally
at if they suffered defeats. And perhaps with
periodic reinforcements from Aman since there would be nothing to
prevent further elvish emigration.