it's not a system if it is concurrent and divisible. the block is the quantum of the bitcoin system.
it's hard to comprehend maybe because you are subjective as a user who creates UTXOs to think of them as like subatomic particles, but they are not. the whole block is a single number. all data can be represented as a number, it doesn't matter that it involves up to 4 megabytes of bits. this is still one number.
if you have to point at two or more things, you aren't talking about a system, you are talking about a process of discovering the next state of the system.
a system is a collection of things, and a quantum is the smallest unit of the WHOLE SYSTEM.
quantum states of electrons are also not singular, but composed of multiple coordinates, and each quantum state consists of a cycle that recurs periodically. thus, the quantum state of bitcoin is the block, as this is the point at which the system is coherent and recognisable. you can't have UTXOs outside of the context of bitcoin, even though you can't have bitcoin without it being made out of UTXOs, the apex of the ontology is the whole system, and the apex of its state is the block. apex is a point, a quantum, the smallest measurable state of the system.
Systems theory - Wikipedia
