I don't know the authors minds so I can't say if they were thinking of the "Hydraulic" versus "Industrial" comparison or not but I doubt it will work as an analogy long term for this series.
I say that because as Mil-tech bard notes what determines how great a percentage of its personal and economic resources a society can devote to war is "its relative level of discretionary economic surplus." In other words how many of its people and how much of its economy must be devoted to keeping the population alive.
A second factor is how much political will there is to spend its discretionary economic surplus on war instead of on the comfort of its people. The issue of political will may keep Arcana from devoting its full resources to the war for a time but if Sharona starts to be a genuine threat to the Arcanan core worlds that will change.
What I want to speculate on is, if the political issues are removed because all Arcanans have come to recognize that they have gotten themselves into a war for survival, how much of its resources can Arcana devote to the war.
Since we haven't seen the Arcanan core worlds yet we have little to speculate on but there is what I believe is a very revealing quote from mul Gurthak's head in Chapter 39 of Hell's Gate. He thinks:
Kelbryan was typical of Ransarans, and there were a lot of them. An appalling number of them, as a matter of fact, when it came to seats in the Union Parliament. Unlike Mythal, which was experiencing a steady decline in population, thanks to the current massive garthan exodus (which had the caste-lords howling in outrage and threatening to impose emigration quotas—as if the Accords would have permitted them to do any such thing), the Ransaran population on Arcana Prime was growing steadily. Not just in absolute terms, but as a percentage of the total planetary population, as well. Despite their much vaunted individualism and the depressing technological advantages it had given them, however, Ransarans as a group tended not to relocate as much as other Arcanans. In part, that was simply because they preferred the creature comforts of home. Given the almost universally high standard of living amongst Ransarans, higher than that of any other group in the Union, outside a few dozen shakira ruling families, Ransarans simply preferred to stay home. Roughing it in a cabin in the wilderness, with no hospitals, no universities, no theaters or museums, no banks or stock exchanges, and no shopping emporia stuffed with luxury goods from every Arcanan universe, was simply too crude for most self-respecting Ransarans. That was one Ransaran attitude mul Gurthak understood perfectly. He missed the comforts of home, as well. Bitterly, at times.
This info dump tells us several things. First, it tells us that free movement of people is part of the Accords. Second, it tells us that Garthans are leaving Mythal at a sufficient rate to affect the balance of power in the Union Parliament. Third, it tells us Andarans and Mythalans tend to move to Arcanas colonies far more often then Ransarans (which could be politically significant if Arcana is ever considering trying to trade land for peace with Sharona). Fourth, it tells us that the large Ransaran population of Arcana enjoys a very high standard of living and describes that standard in language clearly intended to evoke the late 20th and early 21st century consumer driven societies of the developed world on Earth.
I believe that the combination of free movement of people and the "almost universally high standard of living amongst Ransarans" indicates that the Ransaran standard of living cannot be the result of exploiting the rest of Arcanan society. If Andarans or Multhari and Shakira caste Mythalans lived at a greatly lower standard of living then Ransarans I would expect large scale immigration from those societies to Ransar as well and we have no evidence for that. Differences in living standards on the scale of what is found today in the EU, or maybe even a little larger are believable, but they can't be much greater then that. That means the vast majority of Arcanans probably live with a quantity and quality of consumer goods comparable to what is available in the Developed World today.
Such a supply of consumer goods requires a very large "relative level of discretionary economic surplus" and thus shows that Arcana can devote a portion of its economy to war comparable to the portion that an industrial society can. If what I have said above is true then the "Hydraulic" versus "Industrial" comparison cannot apply.
Nicholas