When we read Deuteronomy 32:4 in its full literary context, for example we find that God's tanim work of creation—his "fashioning" of the children of Israel—is revealed precisely in the long, perilous and conflictive process by which human civilizations evolved and the Israelites were brought out of "an empty howling waste" into a land of their own: ...
If the reading I have offered so far is at all correct and God recruits the creation at each stage to play an active, participatory role in what follows, with Adam being charged with an especially vital task of "subduing" other parts of the earth, then there is a very good theological reason why God declares the creation to be "very good" rather than "perfect." The creation cannot be perfect because, in an important sense, it is not entirely God's work. There are principles of freedom at work in the creation, and animals, humans and the earth itself have a God-given roe to play as his coworkers. [Ronald E. Osborn, Death Before the Fall: Biblical Literalism and the Problem of Animal Suffering (Downers Grove, IL: IVP, 2014), 29-31)
With regards to the problem of the creation being described as "very good" but not "perfect," Osborn has put forward an alternative explanation. Creation itself is not perfect because "animals, humans and the earth itself" has to play their parts as God's "coworkers." I confess I do not know what that means, since humans don't actually create anything ex nihilo (assuming Osborn believes in ex nihilo creation), but let's continue on.
The major flaw in Osborn's understanding is that it confuses between creation, and redemption. Creation and redemption are two separate works of God. The first work culminates in Genesis 2: 1-3, where the first Sabbath is celebrated, a prefigurement of the last eternal Sabbath spoken of in Hebrew 4: 1-9, which is the culmination of the second work of redemption. The first work end with a Sabbath which is literarily without an end, and the second work ends with a Sabbath that is literally without an end. The first Sabbath is typological, the second actual. Both are the capstones of God's works.
In the Westminster Standards, the distinction between the two works of God is upheld. From the Westminster Shorter Catechism (WSC):
Q8. How does God executes his decrees?
A. God executes his decrees in the works of creation and providence
Q20. Did God leave all mankind to perish in the estate of sin and misery?
A. God, having out of his mere good pleasure, from all eternity, elected some to everlasting life, did enter into a covenant of grace to deliver them out of the estate of sin and misery, and to bring them into an estate of salvation by a Redeemer.
God executes his decrees in the works of creation and providence (1st work), and then after the Fall, he initiates the work of redemption (2nd work), a work which is not mentioned in WSC Q8. There is a real difference between the two, a distinction and difference which Osborn fails to maintain. If we however maintain that distinction, then it should be clear why God is working now after creation. When God says that His work is complete on Day 7, it means that His work of creation is now complete. After the Fall, God's work of redemption starts, but not His work of creation, which is complete. With regards to the creation of matter ex nihilo, God will not do any such work again, until the Eschaton in the creation of the new heavens and the new earth.
Osborn's proposed solution therefore fails, because he fails to differentiate the two works of God. Does Adam have to "subdue" other parts of creation? Yes, he does, for not all the earth is the paradise of Eden, but that is not creation ex nihilo neither is it to make carnivores herbivores.