I've been busy and unable to reply properly to the thread's premises and surmises.
I should be brief because I think I have to disagree with most everything; to say a lot would be to elaborate negativity.
Let me say this then--I don't think there is any way Tolkien would settle on the idea that Orcs are warped Men. The most important reason has to do with the eternal fate of human beings in Catholic teachings; Tolkien was a very devout Catholic, and highly educated in his own religion as well as on some other subjects. He would never intend anything in his expanded cosmos to contradict core Catholic doctrines. And Catholic orthodoxy is very clear on the nature and destiny of human beings. In this doctrine, we each have an immortal soul, destined for eternal life, and since the Fall of Man, one option is eternal damnation; the other is salvation at the hands of Christ the Redeemer.
There are a lot of potentially problematic aspects to this doctrine, which can cause someone raised to be a devout Catholic themselves, like me, to reject the whole thing and Christianity with it. But in principle, any human being, even those born and raised in highly adverse circumstances, can find salvation.
Therefore if Orcs are in fact twisted humans, their fate is deeply horrifying, for there is no evidence in Tolkien canon anywhere I can think of of even a single Orc seeking, let alone finding, redemption. There are no penitent Orcs, no instances of mercy or even a mere sense of justice being shown by any of them. Therefore the Orcs, if they were truly human at core, are a breed of humans who are damned from conception and exist only to suffer in eternity.
Because Roman Catholic doctrine has nothing definite to say about the status of elves, on the assumption they simply do not exist (and any medieval pronouncements are rendered moot by the claim that "real" elves, in Tolkien's view of them, are quite different than what medieval or ancient churchmen may have believed), Tolkien is much freer to have notions of how a just and gracious God will handle the warped, ruined Elven souls that come before His judgement. Perhaps, having been warped into mere misery, God will simply extinguish them; perhaps some form of opportunity for individual redemption will be offered them sometime in eternity. The question of the ultimate destiny of these evil and repulsive beings is at any rate obscured and mooted by the presumption they derive from Elves instead.
I have other reasons to think this too;
a) In the material world of Arda, Elves are tougher and stronger than Men--therefore the hideous tortures and foul manipulations of their bodies that Melkor would perform on them to batter them into Orcs would be less certain to simply kill them than the same treatment to Men;
b) Elves are of the stuff of Arda, woven into its fate, lacking the mysterious turn to Something Beyond that distinguishes Men; this ought to be helpful;
c) Elves Rule, Men Drool! Which is to say that, while we readers, humans in a Christian age reading a Christian human author, understand that there is a lot about Men that is not apparent to the powers of ancient Arda, in the perspective of the pre-Christian age, Men appear to all observers, themselves included, as a distant second best. Weaker, less wise, mortal, subject to diseases; in every way the Elder Children of Iluvatar appear superior, and mere humans seem to be a cheap knock-off. Compared to the muddy dun of mortal men "doomed to die," Elves are distinctly shiny objects! Why then should Melkor mess around with these breakable apparent Children of a Lesser God, when he can pervert and suborn what is clearly Eru Iluvatar's grandest creation, its natural apex--the Elves?
Now in fact, to Tolkien the Catholic and his post-Resurrection era human readers, the humans turn out to have a lot of claims to consideration, but these will not be known in advance, not even it seems to the faithful, mighty, ancient and wise Valar. Certainly Melkor has no way of anticipating the ultimate role Men will have to play in this cosmos.
d) Why should Melkor invest effort in the long term project of creating a breed of Orcish minions from Men, when Men appear to be very morally as well as physically weak and corruptible just as they are? Indeed it might seem to Melkor that he didn't have to create Orcs at all, for Men seem willing and able to fill the role! Humans as they are are corruptible in ways Elves are not. To get willing service out of Elves Melkor must torture them to the breaking point, but Men are willing to sign on to his campaigns of treachery, murder, and rapine by the horde. Surely Melkor would contemplate "perfecting" the human species to winnow out pity, compassion, mercy, or a sense of justice, but given how willing so many of them are to set these aside for glory and loot and power over others, it can't be a priority.
e) I'd put this point higher, except that it is a matter of canon detail rather than fundamental categories--but in the OTL published accounts anyway, Men come second in time, and by a very long interval too. Melkor has literally ages of time to practice his dark arts upon captured Elves, before the first Men appear. Of course Tolkien could revise that and have both peoples of the Children of Iluvatar be created at the same time; I really don't think he would since the whole concept of "elder" and "younger" people seems pretty central to his whole concept.