You can't simulate that (fundamental randomness) purely classically. The classical world can be simulated with Turing machines, however. And we know infinite pen-and-paper maths can simulate any Turing machine.
How do I get from pen-and-paper maths (doing simple turing-machine-like operations/computations) to a truly random event, a necessary component for a quantum measurement? So when I'm doing my pen-and-paper maths, I have to go grab a radioactive atom and use the time it decays to somehow seed a random event into my simulation.
I do not know of a way to think beyond classically, or beyond the above notion of pen-and-paper maths.
Or are you saying some abstract high-dimensional vector really does ontologically exist in some even higher dimensional space? What space? Not spacetime, that is 4D. And even then how do we reduce that spread out WF to definite values in your ontology.
Math is not an ontology, unless you want to go the Mathematical Universe route.