greatest of the maiar

[Galin]

Well 'greatest threads' seem to hinge on what one means by great of course, but regarding the text, Christopher Tolkien revealed the detail:

'The words in the published text concerning Eonwe, 'whose might in arms is surpassed by none in Arda', were an editorial addition, made in order to prepare for his leadership of the hosts of the West at the Great Battle'.' CJRT, Later Quenta Silmarillion

The text of LQS notes Eonwe as herald of Manwe, and Ilmare handmaid of Varda as chief of the Maiar as we know, and that there are many others without names among Elves and Men, but (thus noted among many others it would seem) 'great and fair was Melian', and wise was Olorin.

As an interesting aside perhaps, in Annals of Aman Este is said to be 'chief of the Maiar'. And in the typescript 'distinct from the amanuensis typescript of the whole work' -- thus distinguished as AAm* -- Nessa and Este are the 'highest among the Maiar' with contemporary emendations to this including the wife of Tulkas being 'Lea the Young' (so that the highest among the Maiar become Lea and Este). For the details of this text AAm* see Morgoth's Ring.