I don't see a future in trying to argue numbers, however. There jus is no way to prove or disprove. Also there is a difference between free men of color and slave still in bondage, and not a good way to seperate them out.
To anyone who grew up in a rural area prior even to WW2, children of families on farms or ranches, or plantations, were pretty restricted in playmates. I have little doubt, a young white CSA soldier would have a slave of a similar age who was as closely bonded to him as any brother might be, maybe more if his own brothers were seperated widely in age. They would have grown up together and shared many adventures or pranks. If the young white man went off to war with a bunch of relative strangers it is within the realm of reasoning to imagine he might be accompanied by his black companion, a real friend who would not in a million years take the first opportunity to "escape", or even have it cross his mind.
Such a slave would want to be armed and his white master would want it too, they would be almost equals in their eyes despite the lowly status outsiders might have for the slave. I have no doubt such a young slave would fight alongside of and fight for his young master until death, despite his status as a slave. A young slave like that, with no knowledge whatsoever of the distant outside world, although realizing his master always has the upperhand, might easily accept things about his social status as just the way the world is, and by far prefer the security what he knows to what he has no real knowledge of. His opinions of Yankee invaders would be exactly as those of his white friend.
(Heck I think we'd even fight side by side with Al-Quiada if green martians invaded to conquer us, no matter our bitter differences).
At any rate, if anyone in authority, like a visiting congressman for instance, ever questioned why this slave here is armed, it would be natural and easy to say, he is just my cook and I've ordered him to go kill us a possum for supper, or somesuch, until the congressman was gone, with smirks behind his back. But if a sudden fight breaks out with a yankee cavalry patrol, that slave would fight as hard against them as anyone, snarling and fighting and shooting to the end I have no doubt.
While I do not disagree with your overall point, my point is, free men of color served openly in some places, and even slaves in bondage served, in some capacity, in many individual units that were under overall CSA control, whether officially acceptable to CSA policy and politicians or not. It is fairly pointless to try to argue the numbers however, but the preponderence of evidence seems to show definitively it was a real exception not the common practice.
To me, the most remarkable feature of this editorial, and the many many many others like it, as well as the actual articles of secession, is how they SELF IDENTIFY, themselves and their cause. "We the Slave-holding States, do join with our sister Slave-holding States, to create a Southern Confederacy of Slave-holding States" etc. etc.
They do not call themselves, the Tariff-hating States or the the Legion of States-Rights States, or the Anti-federalist States of the South, or any number of possibilities. They almost always call themselves the "Slave-holders". To me, self-identity is the most important feature, it is not Northern spin or propaganda.
It is their language, the very specific and deliberately chosen language, they themselves chose time and time again, that they preferred to name themselves, and that they chose to name their own cause with what they themselves saw as their most notable and important distinction from the outsiders who opposed them.
These guys like Hunter even came to the conclusion that Lee had become an abolitionist sympathizer, perhaps tained by West Point, and for that reason dismissed his plea for a major policy change in 1865. These are the CSA politicians who won the fight in congress in 1865 against Lee, and it is these CSA politicians who were still in the upperhand in 1865 that I said they chose Slavery over Independence when the choice was made starkly clear to them by their own military leadership.