[Ivriniel]

But the Valar were not "creators", only "makers" - they had no control over the Flame Imperishable

Not quite true. They could channel the Flame Imperishable into their creations--Telperion, Laurelin, and even the Elves could manifest such 'metaphysical flows'--the Silmarils, the Phial of Galadriel, The Elessar and the Palantiri.

Further, it was Sauronic and Melkorian 'logic' that, I have guessed, manifested the Inverse of the Flame Imperishable--that UNflow of the Flame Imperishable in an inverted, mirror image opposite of the Flame Imperishable. Unlight. The Wraith Dimension. Necromancy. Unlife of the Ringwraiths. Barrow Wights.

If I cast my mind back to the Ainulindale, and our first glimpse of what Illuvatar manifested in the Flame Imperishable, it seems to me that this was some fathoming of a creative purpose, inside a Time-Bound Universe, in accordance with bringing forth something from The Void. I have wondered if Melkor gleaned of means of inverting this essence, by fracturing dimensions of the Spirit World, and then, regiging the system, so that his 'creations' (violations of Manwe-ian manifestations) return something to The Void (life-flow) whilst retaining an echo of sentience. Ringwraiths were not really living, yet had sinew somehow, and they seemed to drain life and somehow 'radiated' fear. Where did their lifeforce actually go? Back to the Void? In Manwe's Halls?

Also, they could not "solve" the problem of evil for two reasons: 1) because they lacked the power to do so (not because they were too incompetent) and 2) because Eru had already solved it: "Arda Healed," which would arrive in the fullness of time.

Here, then, I bring my ideas back to another point. If you are capable of birthing the Sun, what insight do you lack, that you can't fathom Ungoliant's 'organisation' and use a collective effort (I mean, the Valar Combined had a great deal more power than Melkor) to 'flick the UNlight switch' and get her to EXPLODE, rather than SYPHON.

She did have a very fat, bulbous, belly - and it swelled I recall, after eating the light of the Two Trees.

My point is I think the Evil of Melkor could be, and was, reconciled to Eä in order to improve it, but I don't believe it was part of a necessary dynamism [emphasis Ivriniel's] of metaphysical forces, at least not in this dualistic way. Your theories are interesting but I think they're largely precluded by a lot of the content of Morgoth's Ring which I heartily recommend reading in full for a more complete understanding of Professor Tolkien's theodicy (the technical term for answering the problem of evil).

Here, I don't need to rely on the word 'necessary' either. Creation is merely a manifestation of a being's purpose or drive or Song of Creation. So, I do see dynamism of metaphysical forces (and that's a really fantastic way to put it). Dynamism as the interplay of energy (the Flame Imperishable) with metaphysical dimensions conceived by beings on either side of the Good/Evil dualist position. Birthed from the Dynamism--tools for readying Arda for its next majestic manifestation. I imagine that there are ways of organising, deliberately, dynamic flow of what? essences? that are expressions of the Flame Imperishable....