But the fact of choice changes the matter entirely.
And with choice, we need a system of coherence to choose rightly. So systems are practically necessary, because we are free agents. If we are free, we are free from the system of nature. I learned from Richard Weaver that art is our conscious effort to keep from slipping into the illusion that we are not in any way free from nature, but a mere automaton of things as they are. It is interesting to note that this same idea pops up in other venues: we are puppets of some divinity.
I realize that free will has been considered a central issue for hundreds of years, but I simply don't see it as that crucial. The important point IMHO opinion is that God gives each object/creature the freedom to be fully itself. IOW the gift of being is, in all cases, imparted by God without stint or restraint. Each being has available to it the full potential of its being; to be fully and authentically what it is. Choice is secondary. A stone doesn't have "choice" or "will", but it has the full freedom of being nevertheless. If we have free will it's not so much because God "decided" that we should or shouldn't, but rather because it is inherent to the kind of creature we are in the kind of universe we inhabit. If we were some kind of creature to which free will was not naturally implied by the character of our being, then it would be no deprivation that we would lack it.
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).