I think
Ibrin has it on the question of Melkor and Manwë being "coëval".
The
Merriam-Webster definition of "coëval is
Quote:
|
of the same or equal age, antiquity, or duration
|
The Valar are all brethren to one another, as evidenced by the quotes
Form cited.
I therefore take Melkor's special connection with Manwë to mean that they came into being at the same time; the first creations of Ilúvatar. That would in no way conflict with the statements regarding Melkor being the most powerful of the Valar.