I tend to agree with Stultis (post 595)that this may not be so crucial. Even "the reality of human nature" being an illusion may not be so crucial. As you point out, "we need a system of coherence" - not only to choose rightly but to do anything at all. To the extent, I think, that we seem to have free will, we do have free will. And if agency has never been truly, articulately pinned down, we have - to varying degrees - always understood it more or less in this way. Whether we are "puppets of some divinity" or atoms in the void, neither of these possibilities describes our general experience of existence in the world (where if we are sometimes both we are more often neither). For this reason I am inclined to privilege concrete experience (where I feel more agent than puppet) over abstract postulation (where I am equally "free" to be automaton or God Himself).
You want to say it isn't crucial, you say it isn't crucial, and still you face the crux: you choose to privilege concrete experience--and even then you couldn't help but put it in parenthesis as "seeming"--and all the while this sweet and sour mistress called Nature has been carrying you along its own merry way to the grave. Nature is no abstract postulation. Whose concrete experience anyway? I smell the ghost of Descartes, who shrunk his world in the dryer of common reason all for the sake of practical certainty.
Either we resist, resign, or we play illusory games of seeming. The last is chocolate fudge. It's language is sweet and soft.
To the contrary we have Thucydides and Isaiah, who recognize how this weakness becomes useful in the exchange of meaning for meaningless. The good is called bad, the bad is called good. In short, these ancient fuddy duddies are asking us to spell E-V-I-L. And they speak in this way because they appeal not to abstract postulation, but through experience. They say it through the denial of neutrality. Even Heidegger knew technology isn't neutral. And half the dopes on the big court still dream their chocolate fudge of content neutrality. Ignorance is bliss, especially when we privilege a shrunken concrete experience.