Many countries do not, in fact, have lower-level sovereignties with general powers with selective negative limits and a top level sovereign with limited, positive powers.
Very many countries are more like many US states are with their subordinate counties: that is, a top level sovereign with general powers and negative limits with subordinate non-sovereign entities with limited positive powers granted by the top-level sovereigns.
> The United Kingdom, which unlike the United States is quite literally comprised of different countries
"State" is the usual legal term for sovereign juridical entities with territory, while "country" is a less formal term that often corresponds to a state.
(And the "countries" that make up the UK aren't sovereign even in theory, though
some of them have some degree of home rule granted by the central sovereign.)
> the USA is not in some crazy unique position
Unique? No.
But common? Also no.
And it structurally does make solving some problems quite hard, and it makes changing the structure to resolve those problems also hard.
Very many countries are more like many US states are with their subordinate counties: that is, a top level sovereign with general powers and negative limits with subordinate non-sovereign entities with limited positive powers granted by the top-level sovereigns.