It makes sense to me. Illuvatar says in Ainulindale that none may change the Music in his despite, so, any changes would have to be Divinely 'approved', but He 'authorises' men to make changes, which he doesn't even allow the Valar to do. So the Valar are not the same as the Pagan 'gods', but more like Angels, doing Illuvatar's will only, & not able to defy it or change it (meaning that even Melkor & Sauron have only the illusion of freedom). So that would mean that men are given true freedom, when Valar, Maiar & Elves are not. The Valar's role seems to be only to actualise the themes of the Music.
So, because the Fall of Numenor & the re-shaping of the World was not in the original Music (we assume), & was brought about by the rebellion of Men as a result of their freedom, the Valar cannot deal with it, & it has to be brought about by Illuvatar, who is not bound by the Music & can change it. In other words, any change in the Music requires the Valar to lay down their governance of Arda.
Conclusion: Illuvatar has
absolute freedom to act to change the world, Men have freedom to act beyond the dictates of the Music, if permitted to do so by Illuvatar, who has to 'allow' or 'disallow' their choices, & the Valar & Elves' role is to try & actualise the themes of the Music.
Unless I'm completely wrong in my interpretation
