There are good reasons to have counties.
- France has four levels of counties.
- Germany has three levels of counties.
- China has many districts, many of which even have diverging policies about the economy (!)
- Even the Soviets back in their heyday had still things like "the Ukraine" which should decide "local" things.
The central government doesn't want to decide if the village in the woods needs rather a new water pump or a renovation of the road. Those kinds of things are most efficiently decided in the place. If a central government tries to do all this, it will introduce layers of bureaucrats that take ages to decide, or just forget the decision entirely, and the people in that small village will suffer in the meanwhile. The Soviets showed everybody that central planning is not good for everything, only for some things.
What exactly should be done locally and what should be done centrally, is a constantly open question and must be rediscussed eternally. States are not static, but they are dynamic systems; and those dynamics can be surprisingly hard & fast sometimes, especially if they are allowed to build up some momentum over time.
Undercutting this momentum is the strength of the small village governments, as they react fast on changes.
However, sometimes you want momentum for some topics. This has do be done centrally then.
In France, every village decides about the road system themselves. One village boss blocks the idea of a bus or road connection from the neighbor village boss if he likes - this is an example where a LITTLE bit more centralism would be good. On the other hand, they add a teacher to the school in a few weeks if needed; which is good. The doctor's quota is managed centrally in both, France and Germany, or you could better say not managed - way too many child doctors and no available eye doctors since 10 years in France; the other way round in Germany; those are crazy examples for central management gone wrong. Here you have your reason why you want provinces doing some management themselves.
But for Macroeconomics, the Army and other far-reaching systems or strategic decisions; the bigger the deciding body, the better. Without the WHO, there would be no good answer to COVID-19. Imagine the US had only a Texan army, a Californian army, an Arizona army... The world would be a peaceful place and the US would not be so strong.
So for the Army: Bigger = Better.
For your confederacy: a confederation just emphasizes that their parts are as independent as possible, and probably also has stronger decision making on lower level.
But even a centralistic empire, which emphasizes slavery over independence, will still have local decision-makers. The Empress will not decide if you put a new light on the road, after all. The differences are gradual.