The "problem" the writer refers to is the disjunction between two moral systems, and the incompatability of Turin's life-story, which involves both his own bad choices and the whims of fate, and the universe of
the Lord of the Rings, suffused with the presence of a supposedly benevolent creator god. If this god were truly all-knowing (omniscient), all loving (omnibenevolent) and "everywhere at once" (omnipresent) and all-powerful (omnipotent), then surely it follows
logically that he would not allow suffering to occur.
This dilemma exists regardless of what Tolkien actually thought about fate and free will; it seems to me that he never really grappled with this issue with regards to his All-Father, Illuvatar. But he seems to have understood something of it at least implicity. Hence we have competing moral views in both LoTR and CoH, whatever their "intra-text" or "historical" associations. In CoH, Eru, as conceived in the Ainulindale, does not, or cannot, be said to exist. Were he omnipresent, omnibenevolent, omniscient, and omnipotent, he would possess the capability and
desire to save Turin because he is
1. everywhere at once,
2. has an infinitely good will , and so would under no circumstances allow suffering to occur,
3. would know at all times Turin's whereabout and actions and
4. has no restrictions on his power.
Given these premises, Illuvatar could not
logically allow Turin to suffer. That he does so (assuming he exists in Turin's universe) suggests that Illuvatar
lacks one of these qualities altogether, and so is not, in fact, an all powerful, all loving god (and is therefore markedly different to the traditionally conceived Christian god). Of course, there are still problems for LoTR because suffering occurs within the framework of that tale as well. But the problem is more obvious and far more immediately present in CoH.
All this presents an implicit critique of the Christian (or rather, the notion of an all powerful monotheistic) god, strange as that may be in Tolkien's work. Illuvatar simply cannot
logically exist in Turin's universe, unless he lacks one of the "omni" characterstics described above. He can't really exist in the universe of LoTR either, but the issues there are somewhat different.
In LoTR, Tolkien makes a concious attempt to suggest a benevolent power is orchestrating certain events. Thus, we see a more defined system of morality that exists independant of human beings, who are expected to maintain certain moral standards according to this system. As the essayist writes, "...moral agency shifts onto the individual...". In CoH, Turin is still responsible, to some degree, for his actions, although he is not expected to suffer for the sake of some moral cause. In other words, the world of CoH is far more like our own, in that
some suffering has precisely
no moral value at all, and occurs regardless. We may say that this is all the "doing of Morgoth", but this still fails answer the question of why Turin would or even could suffer in a world that is nurtured by an all loving, all powerful and omnipresent god. Once again, we are forced to conclude that Illuvatar
lacks one of these attributes, contrary to the suggestion of the texts, and is thus a far more
limited god, perhaps more powerful that the Valar, but not
infitely powerful. If he
is infinitely powerful, then we must say that he is
not infinitely loving, and is therefore imperfect. In other words, suffering is logically impossible in a world governed by a god who is both infinitely powerful and infinitely loving.
Morgoth's curse exists, to be sure, but as many have pointed out we are never fully aware of the extent to which it actually works, or indeed how it works. Some suffering just happens, because the world is innately cruel, or at least indifferent. That is the similarity that the essayist alludes to with regards to the Oedipus story: Oedipus is not
morally responsible for the tragedy that befalls him, at least not fully. To have moral responsibility implies agency and knowledge, and Oedipus, as well as Turin, lack complete moral agency because they lack complete knowledge. How was Turin to know that Nellas would return to Thingol and speak on his behalf? Given the circumstances, one might contend that his actions were justified, and not rash at all.
Constrast this to the situation in LoTR. The characters' decisions take on a
moral dimension. The suffering depicted LoTR takes on a
moral dimension. That is why it lacks the element of tragedy. Frodo and Sam must suffer because they are doing the
right thing, not merely because the world is harsh. Their suffering attains a kind of cosmological meaning, which in turn suggests their lives are guided by providential
purpose and design. For all of Sauron's diabolical evil, this is still a much more comforting imaginary world than that which
lacks this quality of providentiality.
Still, LoTR does not solve the dilemma described above. God in this world is apparently all loving; he has benevolent intentions and wishes for Sauron to lose his power. However, he is apparently not all powerful, for if this were the case he would logically intervene and destroy Sauron himself (indeed, Sauron would never have arisen in such a universe).
This is the "problem" alluded to by the essayist: "a reader...wonders why such a cruel fate, usually the whim of fickle gods, can befall Túrin Turambar when Eru Ilúvatar is a benevolent creator." In LoTR, a benevolent presence appears to act behind the scenes; in CoH no such force is ever alluded to. A universe with a benevolent god as its creator is a very different one to a universe without such a god, and this is the discrepancy the essayist is referring to. Tolkien imagines alternate cosmologies for his characters to traverse, essentially showing us one where morality is the responsibility of individuals because the universe is the product of a benevolent god. In this universe, individuals can be sure, even
certain in some cases, about the 'correct' moral path. The other universe is one where suffering
just happens, and might lack meaning or

ultimate purpose. Morality still exists, but individuals have less responsibility (not
no responsibility) in this world because they have no final and absolute way of guaging right from wrong. They have responsibility insofar as they can discern the right path, but beyond that there is little certainty.
Morality thus becomes an
epistemic issue: given that no one seems to have access to divine knowledge or guidance in Turin's world (and thus complete knowledge) all choices and actions are undertaken according to provisional standards. The right path may not be the most obvious one; indeed there may not be a right path in some instances, or there may be many. Turin is not guided by a benevolent god, and so is left with his own provisional experience to guide him through the world at large, an experience that is inadequate, ultimately, and leaves him stranded and dying.
That is why the story is tragic: because Turin (and Nienor, and Morwen, and Hurin) are alone and lack the kind of moral certainties that Frodo has access to. Frodo has Gandalf, who tells him that it he was "meant to find the ring", and in some sense also meant to suffer for the sake of its destruction. Turin was never "meant" to do anything: his tragedy is being born into an indifferent world, set upon by a diabolical and monstrous evil and forsaken to face it alone.