And this part destroys it.
To have those bases and KEEP them would require actual force that you can't transport on dragon back. The Chinese eventually have dragons big enough to, but the Romans wouldn't have. Also that ignores Volly being the result of an extra millenium or so of breeding compared to the max the Romans would have had.
Why would this destroy it? Do you believe that the Romans just somehow
forgot what horses, oxen, wagons, and boats were because they had dragons?
And even a particularly small wild dragon is shown to be able to easily carry 20 soldiers in full kit. Even assuming they're puny humans we can reasonably guess these guys were a bare minimum of 200 pounds for man, gun, sword, reloads, and supplies. That means said unusually small wild dragon is hauling around a couple of tons, probably closer to 3 tons if we presume the humans were more human-sized rather than weighing in at the size of adolescents. It would not be particularly difficult for 50 of them transporting 100 tons at a time to make daily flights and get a base supplied in short order, along with transporting 20 guys per dragon to throw a thousand legionnaires at the base in a day. Now have a few more moving between bases half a day apart and you've soon got a fantastic logistics network, especially since this set of options are not exclusive with the network the Romans built in real life, but are just an additional one on top of Roman logistics. Of course, this assumes that mediumweights didn't exist before the breeding programs began, not a certainty given we know there's wild Yellow Reapers and wild Bunyips at least are in the heavyweight category. And for bases near the ocean, ships might transport many thousands of tons to bases near the sea allowing dragons to do fast transport and resupply from there.
Nor is Volly is not the result of an extra millennium of breeding, he's the result of breeding a wild Grey Widowmaker and a domesticated Winchester. He's
one generation removed from completely wild dragons.
Again, are they though? Were Dragons pre Human intervention that big? Every Dragon we see in series(or hear about AFAIR) is post Human Intervention. Now, wild Dragons were probably pretty big before humans, but Elephant sized? As Carnivores? Exceedingly unlikely. Bear sized I'd buy, but you'd need outright magic to justify a carnivore that big before humans start breeding literally perfect prey in massive numbers. And again, if wild Dragons are a serious problem they get dealt with one way or another.
And before you go "but they only need to eat every now and then", that's Courier Weight Dragons and Volly specifically is clearly drawing from Albatross flight strategies, as in, Volly spends most of his air time in a low energy glide, I can buy that, but a brain like Temeraire's is going to demand to be fed often.(honestly even Volly is too smart to actually be low energy)
You keep needing these vague claims that humans will just "deal with" Dragons, but there's nothing backing it up. Humans will be better at targeting sick and weak dragons? Not likely, with their fly speed the dragon can readily nest a hundred miles from the nearest human encampment, across three rivers and on a mountaintop, and the primitive human tribe will have no idea where they even nest, much less be able to somehow travel for weeks to reach it when the dragon can do make the trip in a couple of hours. Humans have no weapon capable of reliably harming them, nor any trap that can reliably work against a creature with near-human intelligence, flight, and a pack social structure. That's on top of some dragons breathing fire or acid, spitting poison or water, and having other weird powers to boot. Humans aren't going to "just deal" with that.
As far as food needs. dragons eat a heck of a lot. But their high fly speed also explains how that works for wild dragons, a dragon can reliably travel faster than any ground-based carnivore can possibly walk and things like rivers, dense forests, and swamps are no barrier to them. The territory of a dragon pack would be absolutely enormous, a tiger might claim a territory of 20x20 miles for its hunting and take days to cover it, but for a wild dragon that's a few minutes gliding, they could claim thousands, even tens of thousands of square miles for a single pack's hunting grounds.
Maybe one of the books I haven't read goes and breaks biology even harder than Dragons do just by existing(I read the first four before I stopped trying to keep up), but at that point you might as well just go "Magic is Real so everything is justified just fine!".
Oh, and before you go "But there's no way they could have a starting point that small", go check out the wild ancestors of Corn or Wheat, honestly, I'd buy that Dragons pre human intervention were wolf sized, we've had crazier results of breeding programs than that.
We see wild dragons in the form of Arkady's crew, and also heavyweight wild Bunyips that can't possibly be the result of human breeding, and are big enough to threaten Temeraire.
Nor would breeding explain things in the timeframe we're talking about. Dragons were bred to their current sizes since domestication during the Roman Empire, which means we've got around 2,000-3,000 years to go from wild dragons to Temeraire. Corn, meanwhile, has been domesticated for at least 9,000 years, perhaps far more than that. Further, a generation of corn is a year while for dragons, significantly longer. Dogs meanwhile have been domesticated for 25-40,000 years and yet we certainly didn't manage to breed them from wolf-sized to monsters bigger than a house, much less in a mere 2000 years, and dogs also have generations of a year or less.
A wolf averages about 80-90 pounds, a Regal Copper hits 100,000 pounds max but averages 60,000, an increase of 665,66.7% over the wolf. Assuming 5 year generations of breeding (feels around the right area) and giving them an extremely generous 3000 years of breeding program, you've got 600 generations. You'd need each dragon to be over 22% bigger than its parents for 600 generations straight, without a single miss to hit that kind of goal. You need far more "magic" to imagine that such a short-timeframe breeding project managed to create modern dragons from something the size of a wolf.
On top of that, we see heavyweight dragons native to Africa and South America, (probably North America but exactly how big Thunderbirds are isn't specified) so this breeding program would somehow have to have succeeded this way multiple times independently. Or... dragons in the wild aren't that tiny.
We see explicitly wild dragons in the form of Arkady and his crew, as well as similar-sized (but heavily armored and spiked) Russian ferals in Siberia later. The assumption that they're somehow really domestic dragons is pure conjecture and flies in the face of statements in the books that these (as well as Grey Widowmakers and a few others) are wild dragons.