[Legate of Amon Lanc]

I have always imagined the "bretheren" really in the sense that they shared similar gifts. And yes, even power. Maybe Melkor was the mightiest of Ainur, but Manwë was right behind him; more importantly, I think when it comes to powers of, say, "govern", counsel, maybe the power of their imagination, mind, all that kind of stuff?

Yes, truth be told, Manwë did not really show us very much, but then again, we are never told about the "daily business of governing Valinor", or the early days of Arda and what's been created from whose initiative etc... I can imagine Manwë being the "nudger" to help others put their plans into shape, or help them and guide them to make their ideas work.

Thinking about e.g. the discussion between Manwë and Yavanna concerning the Ents (and Eagles). From what we know, Manwë certainly enjoys the respect of others and others come to him for counsel - they obviously must act that way based on their experience with him that he is the one who gives them good counsel.

That's nothing against what Form just said about the power and authority (which, if I understood correctly what he has in mind, is a very important notion). But I think the simple dimension of truly having the power and capability - "creative potential" - equal or similar to Melkor's (in its broadness) might be there. We have to put aside the simple clasification of Manwë only as the "lord of winds", which is, I believe, a common mistake and simplification (he simply turned to prefer a certain "portfolio" on top of everything, but nowhere it is told that his capabilities would be limited only to this area - that is in fact most strongly disputed exactly by putting him on the same level with Melkor).